OmeroPy unit tests flake8

This PR fixes the flake8 output on the remaining Python unit tests under `components/tools/OmerPy/test/unit`.

To test this PR:
- check Travis is green (`flake8` is now run on the entire `test/unit` folder)
- check the unit tests are still passing in the next run of http://ci.openmicroscopy.org/job/OMERO-5.0-merge-integration-python/lastCompletedBuild/testReport/