[consutil] Store console port state in STATE_DB

[Blueve]

- What I did

• Console port state now stored in STATE_DB
• Add new exit code(ERR_DISABLE)
• Refactor consutil/lib.py
• Refactor consutil/consutil.py
• Add unit tests for consutil/lib.py

- How I did it

• Refactor origin function to classes
• Refactor origin command implementation with new lib api
• Add 4 new custom exception for error handling
• Take advantage of STATE_DB

- How to verify it
Add unit tests

---------- coverage: platform linux2, python 2.7.16-final-0 ----------
Name                                       Stmts   Miss  Cover
--------------------------------------------------------------
consutil/lib.py                              222     15    93%

Tested on a physical SONiC DUT. Detail steps shown below:

test show command

admin@sonic:~$ sudo consutil show
  Line    Baud    PID    Start Time    Device
------  ------  -----  ------------  --------
     0       -      -             -
     1    9600      -             -
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test connect command

admin@sonic:~$ sudo consutil connect 1
Successful connection to line 1
Press ^A ^X to disconnect

test show brief command (while the line is busy)

admin@sonic:~$ sudo consutil show -b
  Line    Baud    PID                Start Time    Device
------  ------  -----  ------------------------  --------
    *1    9600  18706  Wed Mar  6 09:31:14 2019

test clear command

admin@sonic:~$ sudo consutil clear 1
admin@sonic:~$ sudo consutil show -b
  Line    Baud    PID    Start Time    Device
------  ------  -----  ------------  --------
     1    9600      -             -

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

No change.

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

No change.

[lgtm-com]

This pull request introduces 3 alerts when merging 60b68eb into ef5f212 - view on LGTM.com

new alerts:

• 2 for Unused import
• 1 for Unreachable code

[Blueve]

retest default please