Add ESMPy testing

[bekozi]

Distill correct ESMPy testing. @rokuingh provided these test targets:

ESMPy test targets (python setup.py ):

• test: run the single core unit tests
• test_parallel: run the parallel unit tests
• test_regrid: run only the single core regridding unit tests
• test_regrid_parallel: run only the parallel regridding unit tests
• test_examples: run single core examples
• test_examples: run parallel examples
• test_examples_dryrun: retrieve the data files necessary to run the examples
• test_regrid_from_file: run single core ESMPy enabled regrid from file tests
• test_regrid_from_file_parallel: run parallel ESMPy enabled regrid from file tests
• test_regrid_from_file_dryrun: retrieve data files necessary to run the regrid from file tests
• test_all: run test, test_parallel, test_examples, test_examples_parallel targets

[bekozi]

CircleCI is build everything except test_regrid_from_file. @rokuingh these tests seem pretty intensive. Are they necessary/required? I wonder if they are something used primarily for development.

[rokuingh]

@bekozi, no these tests are not for development, but they are the same tests run by ESMF_RegridWeightGenCheck, just using the ESMPy interfaces. They are costly so maybe the best solution is to reduce the number of tests to something like 10, instead of the 100+ currently run.