Unit tests for #999 (k8s cache PodProcessor infinite loop issue)

[Kami]

This pull request is based on top of #999 and adds some basic mock based (regression) unit tests for a bug fix in #999.

Also having end to end tests would be ideal, but setting up the environment to be able to exercise this code path in the end to end tests would be quite cumbersome.

TODO

• Changelog entry

[codecov]

Codecov Report

Merging #1004 (4306f6c) into master (b98e8a6) will increase coverage by 0.03%.
The diff coverage is 87.01%.

@@            Coverage Diff             @@
##           master    #1004      +/-   ##
==========================================
+ Coverage   79.94%   79.97%   +0.03%     
==========================================
  Files         181      181              
  Lines       41654    41731      +77     
  Branches     4679     4688       +9     
==========================================
+ Hits        33299    33372      +73     
- Misses       7218     7222       +4     
  Partials     1137     1137              

Impacted Files	Coverage Δ
tests/unit/monitor_utils/k8s_test.py	95.94% <86.49%> (-1.24%)	⬇️
scalyr_agent/monitor_utils/k8s.py	79.54% <100.00%> (+0.61%)	⬆️
scalyr_agent/copying_manager/copying_manager.py	85.34% <0.00%> (-0.66%)	⬇️
scalyr_agent/builtin_monitors/docker_monitor.py	75.69% <0.00%> (+0.48%)	⬆️

[github-actions]

Test Results

       33 files  ±0         33 suites  ±0   59m 45s ⏱️ + 3m 18s
  1 405 tests +1    1 394 ✔️ ±0    10 💤 ±0  1 ❌ +1 
10 824 runs  +8  10 596 ✔️ +7  227 💤 ±0  1 ❌ +1 

For more details on these failures, see this check.

Results for commit 4306f6c. ± Comparison against base commit b98e8a6.

♻️ This comment has been updated with latest results.