Only set a user's password during unit tests if one is provided.
Review Request #10887 — Created Feb. 6, 2020 and submitted
TestCase.create_user()was unconditionally setting a user's password,
but if a password wasn't provided, the end result wasn't really correct.
We ran into this on RBCommons and fixed it there, but this fix is worth
backporting to Review Board.
This change simply makes the
set_password()call conditional on
whether a password was provided.
Unit tests passed.