Support finding suite class that is not defined in the main module.

[mhaoli]

Background: Current implementation only searches for the test suite class in the __main__ module. But projects like BeToCQ are running in a different approach, which causes that test suite class is not in the __main__ module.

Change: When suite class is not found in the main module, search for it in the module of the caller of suite_runner.run_suite_class.

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This change is 

[xianyuanjia]

Reviewed 3 of 3 files at r1, all commit messages.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @mhaoli and @xpconanfan)

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mobly/suite_runner.py line 185 at r1 (raw file):

    if len(stacks) < 2:
      logging.debug(
          f'Failed to get the caller stack of run_suite_class. Got stacks: %s',

Nit: this is not a f-string

Code quote:

f

[mhaoli]

Reviewable status: 2 of 3 files reviewed, all discussions resolved (waiting on @xianyuanjia and @xpconanfan)

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mobly/suite_runner.py line 185 at r1 (raw file):

Previously, xianyuanjia wrote…

Nit: this is not a f-string

Thanks. DONE.

[xianyuanjia]

Reviewable status: 1 of 3 files reviewed, all discussions resolved (waiting on @xpconanfan)