Add setup.cfg file at the root of OmeroPy test/ and simplify Travis

As @ximenesuk is starting to validate the integration tests to comply with `flake8`, this PR proposes to add a `setup.cfg` at the root of the `components/tools/OmeroPy/test` folder. 
This way:
- `flake8` can simply be run as `flake8 -v components/tools/OmeroPy/test` 
- files validation can be  checked by updating the exclude list and re-running the command above
- no further change needs to be added to the validation of the `test` folder in the Travis script