Various changes to accomodate running tests (including integration tests)

This is just an idea, I'm making a lot of assumptions, so I'm not expecting you to merge this as is. The main aim is just to make it easy to run tests in a vagrant environment.

For a start I've added a TESTING flag to `settings.py`, I don't know what you think about that. The other big thing is tweaking the integration tests setup code to accommodate installations where a superuser has already been registered. I don't know what you're going to think about that either. The other little tweak is raising the deis user's permissions in provisioner script to allow creation of the ephemeral test DBs. There's also some additions to the documentation to explain things.

BTW, I have tested this on my environment and it runs the tests correctly identifies broken code.

Feel free to take or leave whatever feels useful.