MockTestBase for service client based test methods

Goal: Run tests locally

Now: Run with environment variable `management.recording=true` will record all traffic in all test methods. Run with environment variable `management.mocked=true` will do the playback.

To do: Mock for non-service clients, e.g. storage clients.
I think that'd be a good idea. @ljhljh235 what do you think the t-shirt complexity of this would be to do?