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
the "same" comments probably aren't relevant -- the `.proxy()` fix to linking makes these tests all come out the same as in OMERO.web