Turn python test scripts into proper TESTS elements
Right now we use the check-local target to run the python unit tests. But that's kinda janky; we could be doing better if we had them be part of TESTS, which is feasible if we do the right automake incantations.
See https://www.gnu.org/software/automake/manual/html_node/Parallel-Test-Harness.html for some tips on how to do this properly.