DockerLatentWorker: Handle not found exception when stopping

[cmouse]

Contributor Checklist:

• I have updated the unit tests
• I have created a file in the master/buildbot/newsfragments directory (and read the README.txt in that directory)
• I have updated the appropriate documentation

If there is e.g. connectivity problem to the docker host, ensure we handle exceptions when stopping worker, otherwise the substantiation gets stuck on preparing worker.

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[cmouse]

I'll look into this in few weeks.

[cmouse]

Updated to catch the exception that's actually causing the problems.

[codecov]

Codecov Report

Merging #5308 (7ad38db) into master (f5df7b0) will decrease coverage by 0.16%.
The diff coverage is 40.00%.

❗ Current head 7ad38db differs from pull request most recent head ce4af77. Consider uploading reports for the commit ce4af77 to get more accurate results

@@            Coverage Diff             @@
##           master    #5308      +/-   ##
==========================================
- Coverage   91.82%   91.66%   -0.17%     
==========================================
  Files         340      340              
  Lines       36371    36375       +4     
==========================================
- Hits        33398    33342      -56     
- Misses       2973     3033      +60     

Impacted Files	Coverage Δ
master/buildbot/worker/docker.py	82.66% <40.00%> (-0.60%)	⬇️
master/buildbot/__init__.py	76.92% <0.00%> (-15.39%)	⬇️
worker/buildbot_worker/__init__.py	77.61% <0.00%> (-14.93%)	⬇️
.../migrate/versions/048_change_properties_to_text.py	87.50% <0.00%> (-12.50%)	⬇️
...migrate/versions/046_mysql_innodb_compatibility.py	89.47% <0.00%> (-10.53%)	⬇️
master/buildbot/db/test_results.py	89.54% <0.00%> (-6.54%)	⬇️
master/buildbot/db/enginestrategy.py	69.17% <0.00%> (-5.48%)	⬇️
...dbot/db/migrate/versions/052_cascading_set_null.py	94.00% <0.00%> (-4.00%)	⬇️
master/buildbot/process/botmaster.py	94.64% <0.00%> (-3.58%)	⬇️
master/buildbot/db/connector.py	96.51% <0.00%> (-3.49%)	⬇️
... and 1 more

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[cmouse]

@tardyp @p12tic something I should do this to this?

[p12tic]

@cmouse Sorry for missing this PR. It looks good to me in principle. Could we add tests to cover this new behaviour? There's already a number of tests in test_docker.py, it shouldn't be complex to extend that.