[unit test][pfcwd] Fix tests that require sudo access

[smaheshm]

- What I did
The 'config' tests that require sudo access were failing. Fixed it by mocking os.geteuid.

- How I did it
Fixed it my mocking os.geteuid.

- How to verify it
Unit tests and manual verification

before:

samaddik@856d790db1d1:/sonic/src/sonic-utilities/tests$ pytest-3 pfcwd_test.py  -k test_pfcwd_start_actions_masic
>       assert result.exit_code == 0                                                                                                                                                                                                         |
E       AssertionError: assert 1 == 0                                                                                                                                                                                                        |
E        +  where 1 = <Result SystemExit('Root privileges are required for this operation')>.exit_code                                                                                                                                       |
                                                                                                                                                                                                                                             |
pfcwd_test.py:335: AssertionError                                                                                                                                                                                                            |
----------------------------------------------------------------------------------------------------------- Captured stdout setup -----------------------------------------------------------------------------------------------------------|
SETUP                                                                                                                                                                                                                                        |
----------------------------------------------------------------------------------------------------------- Captured stdout call ------------------------------------------------------------------------------------------------------------|
Changed polling interval to 199ms on asic0                                                                                                                                                                                                   |
BIG_RED_SWITCH status is enable on asic0                                                                                                                                                                                                     |
Changed polling interval to 199ms on asic1                                                                                                                                                                                                   |
BIG_RED_SWITCH status is enable on asic1                                                                                                                                                                                                     |
          PORT    ACTION    DETECTION TIME    RESTORATION TIME                                                                                                                                                                               |
--------------  --------  ----------------  ------------------                                                                                                                                                                               |
     Ethernet0      drop               200                 200                                                                                                                                                                               |
     Ethernet4      drop               200                 200                                                                                                                                                                               |
  Ethernet-BP0      drop               200                 200                                                                                                                                                                               |
  Ethernet-BP4      drop               200                 200                                                                                                                                                                               |
Ethernet-BP256      drop               200                 200                                                                                                                                                                               |
Ethernet-BP260      drop               200                 200                                                                                                                                                                               |
                                                                                                                                                                                                                                             |
Root privileges are required for this operation                                                                                                                                                                                              |
                                                                                                                                                                                                                                             |
--------------------------------------------------------------------------------------------------------- Captured stdout teardown ----------------------------------------------------------------------------------------------------------|
TEARDOWN                                                                                                                                                                                                                                     |
================================================================================================== 1 failed, 17 deselected in 0.18 seconds ==================================================================================================|

After:
============================================================================================================ test session starts ============================================================================================================|
platform linux -- Python 3.7.3, pytest-3.10.1, py-1.7.0, pluggy-0.8.0
rootdir: /sonic/src/sonic-utilities/tests, inifile: pytest.ini
plugins: cov-2.6.0
collected 18 items / 17 deselected                                                                                                                                                                                                          

pfcwd_test.py .                                                                                                                                                                                                                       [100%]

================================================================================================== 1 passed, 17 deselected in 0.22 seconds ==================================================================================================

samaddik@856d790db1d1:/sonic/src/sonic-utilities/tests$ pytest-3 pfcwd_test.py -k test_pfcwd_start_actions_masic

- Previous command output (if the output of a command-line utility has changed)

- New command output (if the output of a command-line utility has changed)

[jleveque]

unittest is part of the standard library. Please move this line to the bottom of the first group of imports, e.g.,

import imp
import os
import sys
from unittest.mock import patch

[smaheshm]

retest this please

[smaheshm]

retest this please