MDL-35332: Fix bug preventing admin setting password on install
MDL-35332: Cache bcrypt support to avoid re-running crypt()
MDL-35332: Ensure password_compat tests run
MDL-35332: Prevent password_compact unit tests running if not supported
MDL-35332: Set prefix during unit tests

Initially I removed this but I'm putting it back as it produced some
warnings when running the tests.