Fix web API feature tests when running entire suite
Review Request #9178 - Created Sept. 7, 2017 and submitted
When running the entire RB suite (or more than just
reviewboard.webapi.tests.test_base), the feature unit tests would fail
due to not being able to
reverse()URLs for the testing resources.
This was because the URLs were being cached and therefore the lookups
were failing. We now clean the URL cache during these test runs to
ensure they run correctly.
Ran unit tests.