[GCU] Update dhcp_relay to ensure a clean test env

[wen587]

Description of PR

Summary:
Fixes # (issue)

Type of change

• Bug fix
• Testbed and Framework(new/improvement)
• Test case(new/improvement)

Back port request

• 201911
• 202012
• 202205
• 202305

Approach

What is the motivation for this PR?

How did you do it?

How did you verify/test it?

Any platform specific information?

Supported testbed topology if it's a new test case?

Documentation

[mssonicbld]

The pre-commit check detected issues in the files touched by this pull request.
The pre-commit check is a mandatory check, please fix detected issues.

Detailed pre-commit check results:
trim trailing whitespace.................................................Passed
fix end of files.........................................................Passed
check yaml...........................................(no files to check)Skipped
check for added large files..............................................Passed
check python ast.........................................................Failed
- hook id: check-ast
- exit code: 1

tests/generic_config_updater/test_dhcp_relay.py: failed parsing with CPython 3.8.10:

Traceback (most recent call last):
File "/home/AzDevOps/.cache/pre-commit/repo3_b41alu/py_env-python3/lib/python3.8/site-packages/pre_commit_hooks/check_ast.py", line 21, in main
ast.parse(f.read(), filename=filename)
File "/usr/lib/python3.8/ast.py", line 47, in parse
return compile(source, filename, mode, flags,
File "tests/generic_config_updater/test_dhcp_relay.py", line 254
def test_dhcp_relay_suite(rand_selected_dut, vlan_intfs_list)
^
SyntaxError: invalid syntax
...
[truncated extra lines, please run pre-commit locally to view full check results]

To run the pre-commit checks locally, you can follow below steps:

1. Ensure that default python is python3. In sonic-mgmt docker container, default python is python2. You can run
   the check by activating the python3 virtual environment in sonic-mgmt docker container or outside of sonic-mgmt
   docker container.
2. Ensure that the pre-commit package is installed:

sudo pip install pre-commit

3. Go to repository root folder
4. Install the pre-commit hooks:

pre-commit install

5. Use pre-commit to check staged file:

pre-commit

6. Alternatively, you can check committed files using:

pre-commit run --from-ref <commit_id> --to-ref <commit_id>

[mssonicbld]

The pre-commit check detected issues in the files touched by this pull request.
The pre-commit check is a mandatory check, please fix detected issues.

Detailed pre-commit check results:
trim trailing whitespace.................................................Passed
fix end of files.........................................................Passed
check yaml...........................................(no files to check)Skipped
check for added large files..............................................Passed
check python ast.........................................................Passed
flake8...................................................................Failed
- hook id: flake8
- exit code: 1

tests/generic_config_updater/test_dhcp_relay.py:260:1: E302 expected 2 blank lines, found 1

flake8...............................................(no files to check)Skipped
check conditional mark sort..........................(no files to check)Skipped

To run the pre-commit checks locally, you can follow below steps:

1. Ensure that default python is python3. In sonic-mgmt docker container, default python is python2. You can run
   the check by activating the python3 virtual environment in sonic-mgmt docker container or outside of sonic-mgmt
   docker container.
2. Ensure that the pre-commit package is installed:

sudo pip install pre-commit

3. Go to repository root folder
4. Install the pre-commit hooks:

pre-commit install

5. Use pre-commit to check staged file:

pre-commit

6. Alternatively, you can check committed files using:

pre-commit run --from-ref <commit_id> --to-ref <commit_id>