Add chgrp/delete Python tests (assist #12452 and #12544).

This is a PR that moves test outlined in https://trac.openmicroscopy.org.uk/ome/ticket/12452 from @dpwrussell's https://gist.github.com/dpwrussell/6aa271b5c88a106c6f4a to the OmeroPy test suite. It also adds the test from https://trac.openmicroscopy.org.uk/ome/ticket/12544.

Outstanding questions:
1) Tests that fail have been marked with `@xfail`. What's tricky, is that I'm not sure if those failures are expected. That should be the main point of this PR.

To test: verify that code makes sense and that the Python integration tests are still green.

/cc @joshmoore, @mtbc
My take on this is https://trac.openmicroscopy.org.uk/ome/ticket/12452#comment:11 -- while I doubted that, for instance, Douglas' second test is something that should ever pass, there are certainly a few `@xfail`s here that I would expect my https://github.com/mtbc/openmicroscopy/tree/trac-11779-graphs branch to fix or, more probably, to already have fixed.