[WIP] add benchmarks for joblib+distributed (+scikit-learn)

[pierreglaser]

Still WIP, I only pushed the source files of the benchmark, and not the asv metadata files.

[codecov]

Codecov Report

Merging #1077 into master will decrease coverage by 0.27%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1077      +/-   ##
==========================================
- Coverage   94.45%   94.17%   -0.28%     
==========================================
  Files          47       47              
  Lines        6889     6889              
==========================================
- Hits         6507     6488      -19     
- Misses        382      401      +19     

Impacted Files	Coverage Δ
joblib/test/testutils.py	50.00% <0.00%> (-50.00%)	⬇️
joblib/test/test_parallel.py	95.50% <0.00%> (-1.66%)	⬇️
joblib/test/test_dask.py	97.99% <0.00%> (-0.81%)	⬇️

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