KM Multi-threaded stress tests - Code clean-up, duplicate code refactoring

[dv-msft]

Description

Code clean-up and common code refactoring of the tests in the 'Kernel mode Multi-threaded stress tests' suite.

Testing

clean-up of existing test collateral.

Documentation

No doc changes.

Fixes #2463

[codecov]

Codecov Report

Merging #2467 (56e1938) into main (174757e) will decrease coverage by 0.06%.
The diff coverage is n/a.

❗ Current head 56e1938 differs from pull request most recent head e59e7ee. Consider uploading reports for the commit e59e7ee to get more accurate results

@@            Coverage Diff             @@
##             main    #2467      +/-   ##
==========================================
- Coverage   84.02%   83.97%   -0.06%     
==========================================
  Files         155      155              
  Lines       28868    28868              
==========================================
- Hits        24257    24242      -15     
- Misses       4611     4626      +15     

see 4 files with indirect coverage changes

[dthaler]

This implies the test is non-deterministic and if the CPU is pegged then the test can fail, is that correct? If so, there's probably a better solution in the future than introducing an arbitrary delay.

[dv-msft]

No, the test itself wouldn't fail. It would just carry on with the start of the 'extension restart' thread delayed even further. Given that the minimum test runtime is 1 minute, IMO it's more than enough for the restart thread to start running eventually. In any case, system load affecting thread scheduling would affect the test threads as well, so their delays would balance out.

FWIW, I did think of synchronizing this thread with the test threads but thought it was overkill given the 'test only' nature of this code. But I can certainly file an issue to revisit that synchronization if it is seen to cause issues during actual testing.