Speed up tests for apps using clearance with bcrypt

If clearance detects that it's being run in the test environment, it
will lower the bcyrpt cost factor (essentially, how much it will sleep)
to the minimum.

On my machine, this change took the test suite time from ~30 seconds to ~7. Those results aren't typical. For whatever reason, bcrypt is just dog slow on my machine. However, other developers on the project saw their suite times go from ~10 to ~6 seconds.