Fix KeyError: u'MUX_LINKMGR' when comparing pre config and current config

[ZhaohuiS]

Signed-off-by: Zhaohui Sun zhaohuisun@microsoft.com

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

Approach

What is the motivation for this PR?

Some test cases failed at teardown when comparing pre config and current config:

                    for key in cur_config_extra_keys:
>                       cur_only_config[duthost.hostname].update({key: cur_running_config[key]})
E                       KeyError: u'MUX_LINKMGR'

The issue is introduced by #6527.

How did you do it?

Get previous and current config keys after removing exclusive keys.
Also add [cfg_context] for cur_only_config and pre_only_config

How did you verify/test it?

Run dualtor case,such as dualtor/test_tor_ecn.py::test_dscp_to_queue_during_encap_on_standby

Any platform specific information?

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

Documentation

[azure-pipelines]

The pre-commit check detected issues in the files touched by this pull request.
The detected issues may be old or new. For new issues, please try to fix them.

For old issues, it is not mandatory to fix them because they were not caused by this change. It is unfair to blame
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Detailed pre-commit check results:
trim trailing whitespace.................................................Failed
- hook id: trailing-whitespace
- exit code: 1
- files were modified by this hook

Fixing tests/conftest.py

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/conftest.py:1854:121: E501 line too long (155 > 120 characters)
tests/conftest.py:1855:121: E501 line too long (155 > 120 characters)
tests/conftest.py:1856:121: E501 line too long (128 > 120 characters)

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