Turn down parallel job logging messages

[brenmous]

This ties to the joblib verbosity to the PyRate verobisty - joblib messages will be disabled unless "DEBUG" is set as log level. I've also removed the MPI warning by setting an environment variable in the init of the pyrate module.

[codecov-io]

Codecov Report

Merging #224 into develop will decrease coverage by 0.01%. The diff coverage is 87.5%.

@@             Coverage Diff             @@
##           develop     #224      +/-   ##
===========================================
- Coverage    83.97%   83.96%   -0.02%     
===========================================
  Files           24       24              
  Lines         2914     2924      +10     
===========================================
+ Hits          2447     2455       +8     
- Misses         467      469       +2

Impacted Files	Coverage Δ
pyrate/scripts/main.py	0% <0%> (ø)	:arrow_up:
pyrate/scripts/run_prepifg.py	93.84% <100%> (ø)	:arrow_up:
pyrate/linrate.py	98.66% <100%> (+0.01%)	:arrow_up:
pyrate/config.py	89.69% <100%> (+0.05%)	:arrow_up:
pyrate/scripts/converttogtif.py	93.54% <100%> (ø)	:arrow_up:
pyrate/timeseries.py	91.78% <100%> (+0.05%)	:arrow_up:
pyrate/orbital.py	93.02% <100%> (ø)	:arrow_up:
pyrate/mst.py	98.05% <100%> (ø)	:arrow_up:
pyrate/ref_phs_est.py	93.9% <100%> (ø)	:arrow_up:
pyrate/__init__.py	100% <100%> (ø)	:arrow_up:
... and 2 more

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