Fix flake8 warnings/errors in test_jit.py (#16409)

Fix flake8 warnings/errors in test_jit.py (#16409)

Summary:
These were really annoying to see in the phabricator UI when trying to land PRs that touched test_jit.py, so this fixes them.

One remaining item is the T484 error. Locally, flake8 still chokes on that line even though I put the noqa comment there (and tried varying whitespaces around it etc). Not sure why it still persists...
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16409

Differential Revision: D13832658

Pulled By: jamesr66a

fbshipit-source-id: 46356ba6444ae5ee1a141c28489bdcc7c99e39c0