This change implements support for registry integration tests using the new py.test-based live server test fixture. We can now parametrize the protocols we use (in prep for V2_2), and it makes the code *much* cleaner and less hacky.
Note that moving the vast majority of the tests over from the existing impl will come as a followup PR
This allow us to super-easily instantiate a live, running Flask server with the test app, as well as interact with it, without any of the crazy boilerplate we previously used
