Better exception handling in tests

[rotu]

1. Don't continue with testing if an extension crashes
2. Use logger.exception to format current traceback in an error

[codecov]

Codecov Report

Merging #322 into master will increase coverage by 0.03%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #322      +/-   ##
==========================================
+ Coverage   79.61%   79.65%   +0.03%     
==========================================
  Files          55       55              
  Lines        3209     3209              
  Branches      534      534              
==========================================
+ Hits         2555     2556       +1     
+ Misses        607      606       -1     
  Partials       47       47              

Impacted Files	Coverage Δ
colcon_core/task/python/test/__init__.py	26.59% <0.00%> (+0.27%)	⬆️
colcon_core/command.py	86.91% <0.00%> (+0.06%)	⬆️

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[dirk-thomas]

Don't continue with testing if an extension crashes
Use logger.exception to format current traceback in an error

(As mentioned a few times to you already) Please consider creating separate pull requests for orthogonal changes - simply because each can be reviewed and iterated on independently.

Regarding the functional change: a very important design choice / feature of colcon is that a single extension (which can be provided by any package) does rarely result in a fatal error of the tool. In as many cases as possible colcon tries to be resilient, logs the error, but continue to perform the requested operation. Therefore I don't think patch is the right approach to resolve #321.