Cleanup base tests
Cleanup base tests

``pytest.importorskip`` wasn't being used properly, would result in
whole file skipping if any were skipped. Fixed, and cleaned up imports
and a few pep8 things.

mraspaud/dask,ContinuumIO/dask,chrisbarber/dask,mikegraham/dask,mraspaud/dask,jcrist/dask,dask/dask,mrocklin/dask,blaze/dask,dask/dask,mrocklin/dask,cowlicks/dask,jcrist/dask,jakirkham/dask,blaze/dask,jakirkham/dask,gameduell/dask,ContinuumIO/dask,cpcloud/dask