OmeroPy: src flake8 (II)

Follow up of https://github.com/openmicroscopy/openmicroscopy/pull/2902. 

To review this PR:

 - check Travis is green and/or that `omero/scripst.py` and `omero.processor.py` pass `flake8` without warning
- check the integration tests are still passing
- test scripts still work as expected.

/cc @ximenesuk

--no-rebase