sanity check fixes for chassis; and cache cleanup at the end of pytest session

[sanmalho-git]

Description of PR

Summary:
Fixes # (issue)

Type of change

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

Approach

What is the motivation for this PR?

• sanity check:

  • The BGP and interface sanity checks for multi-dut were changed to iterate through all the nodes in a multi-dut setup. However, for a T2 chassis, the multi-dut testbed contains a supervisor card as well, which doesn't have any BGP/PORT configuration. Thus, these checks fail for supervisor card.

• cache cleanup:

  • If we change the inventory file and re-run pytest, the old cached data for the inventory is used instead of picking up the changes.

How did you do it?

• sanity_check:
  • Iterate through frontend_nodes of duthosts instead of all the nodes.
• cache cleanup:
  • Added fixture cleanup_cache_for_session that is called at the beginning of a session to remove the cached facts for all the DUTs in the testbed. This is not an automatic fixture, and is needed in the following scenarios:
    • Running tests where some 'facts' about the DUT that get cached are changed.
    • Running tests/regression without running test_pretest which has a test to clean up cache (PR#2978)
    • Test case development phase to work out testbed information changes.

How did you verify/test it?

Any platform specific information?

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

Documentation

[yxieca]

@sanmalho-git I think your cache removal code has legit use cases. I suggest: make it not auto use, so test case developer can temporarily reference it until the test case is stable. Change the clean up to before test so that the testcase don't have to fail once before cleanup.

[yxieca]

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