OmeroPy: src flake8 (I)

See https://trello.com/c/vnojR45Q/43-flake8-omeropy. This PR is the first of a series dedicated to have `components/tools/OmeroPy/src` compliant with the PEP-8 style.

To review this PR:

- check Travis is green, especially that `flake8 -v components/tools/OmeroPy/src`  validates the files modified by this PR
- check the integration tests are still passing

/cc @ximenesuk