Log mapper and reducer stderr

[awdeorio]

Send stderr produced by mapper or reducer to logger.warning.

We suggest writing debug messages to stderr. However, stderr is swallowed unless there's a non-zero exit. Instead, we should pass this output through to the user.

Validation

Start with a sample MapReduce program. Edit map.py and reduce.py to write the stderr. Then run. ALso try with verbose.

$ madoop --example
$ madoop \
  -input example/input \
  -output example/output \
  -mapper example/map.py \
  -reducer example/reduce.py

$ madoop \
  --verbose \
  -input example/input \
  -output example/output \
  -mapper example/map.py \
  -reducer example/reduce.py

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.18%. Comparing base (0bbffe2) to head (2abbd1e).
⚠️ Report is 19 commits behind head on develop.

Files with missing lines	Patch %	Lines
madoop/mapreduce.py	75.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           develop      #86       +/-   ##
============================================
- Coverage    96.98%   79.18%   -17.80%     
============================================
  Files            4        4               
  Lines          265      269        +4     
============================================
- Hits           257      213       -44     
- Misses           8       56       +48     

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[garv8]

LGTM, is it safe to merge with the Codecov test failing?