remove leftover files when rerunning unit tests

[rstaten]

This PR addresses #774, removing temporary files generated by QuickLook unit tests that are not removed if test_ql_qa.py is killed while running.

• Note: only the files test-pix-abcde.fits and test-raw-abcde.fits mentioned in Unit tests don't clean up QA fits files automatically #774 are removed as the other files are not generated by test_ql_ql.py.

@rkehoe, @sbailey Please review and/or provide any necessary additional comments.

[rkehoe]

Thanks @rstaten. Looks fine as a first pass. As we discussed, a more robust solution may be to develop a signal handler for this, but that should be contingent on QL development questions still TBD elsewhere. This at least removes the item that was thwarting others. So if @sbailey is okay with it as a first pass, I’m okay with it.