Finish Phobos Integration

We have a Phobos plugin but haven't run it against real phobos.

Task is to fill out the Python phobos e2e tests in the style of our other e2e tests (probably using s3 frontend when ready).

The main thing here is getting a phobos instance running - I had some issues with their db setup scripts, we may need to set up the db ourselves for these tests.