Rename paralleltest_distarray to paralleltest_localarray.
Shorten test docstrings.
Refactor localarray tests.

Add an `MpiTestCase` base class and use the `comm_null_passes` decorator.
Refactor testing infrastructure.

Also, refactor DAP tests to use it.

Mainly, add a `testing.py` with an `MpiTestCase` and `comm_null_passes` decorator.
Refactor paralleltest_functions.
Refactor test_maps.

1. It's not actually a paralleltest
2. Just shorten some docstrings
Refactor paralleltest_ndenumerate.
Refactor paralleltest_umath.
Remove a blank line.
Refactor paralleltest_nprand.
Reorder a method for consistency.
Merge branch 'odin' into feature/refactor-tests