Removing pytables exception

This removes an odd special handling of basic testing because of missing wheels in pytables in 3.7. It turns out that this is (no longer?) necessary. It also moves the basic python test script into the actual test setup. It was currently extracted to accomodate python 2.7 tests.

!856 (merged) also requires this change @ethan.payne , so you can merge that into your MR.