Simplifications for Praefect-based tests
This MR refactors our Praefect-based tests to build the Praefect binary ad-hoc instead of using a Makefile prerequisite. This aligns with all our other binaries, and furthermore it makes it easier to test with Praefect in an IDE. While at it, I'm also fixing an issue we have with how we modify the environment in tests to turn of forced creation of repository entries in the DB during tests.