Parallelize functions in test modules

[jdebacker]

This PR updates test modules with longer running tests to set up and use a dask client with multiple workers.

[codecov-io]

Codecov Report

Merging #557 into master will decrease coverage by 0.23%.
The diff coverage is 64.83%.

@@            Coverage Diff             @@
##           master     #557      +/-   ##
==========================================
- Coverage   80.48%   80.24%   -0.24%     
==========================================
  Files          47       47              
  Lines        6420     6500      +80     
==========================================
+ Hits         5167     5216      +49     
- Misses       1253     1284      +31     

Impacted Files	Coverage Δ
ogusa/tests/test_basic.py	41.02% <44.44%> (+1.02%)	⬆️
ogusa/tests/test_execute.py	68.18% <44.44%> (-16.44%)	⬇️
ogusa/tests/test_startyears.py	50.00% <44.44%> (-7.15%)	⬇️
ogusa/tests/test_txfunc.py	65.07% <44.44%> (-1.59%)	⬇️
ogusa/tests/test_user_inputs.py	60.71% <44.44%> (-7.71%)	⬇️
ogusa/tests/test_run_ogusa.py	32.65% <50.00%> (+2.65%)	⬆️
ogusa/tests/test_TPI.py	59.33% <92.30%> (+2.59%)	⬆️
ogusa/tests/test_SS.py	96.29% <92.85%> (+0.10%)	⬆️
ogusa/tests/test_get_micro_data.py	82.66% <100.00%> (+2.36%)	⬆️
ogusa/get_micro_data.py	98.21% <0.00%> (-1.79%)	⬇️

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[jdebacker]

Hmm, initial commits passed on Travis CI, but I was getting a local failure due with an error message suggesting too many processes were open.

Now working off some examples from this dask distributed issue to try to open up and tear down a dask client separately for each module.

[jdebacker]

@rickecon Full test suite seems to run through well (and much faster) locally. There are some declines in code coverage for instances of functions that are not run on Travis CI and where additional lines were added to pass the dask client. This is ready for you to review.

[rickecon]

Really nice @jdebacker .