Fix the occasional failed test in extensions.
Review Request #7438 — Created June 19, 2015 and submitted
We had an extension-related test that would try to simulate two threads trying to install media files at the same time, to ensure our locks were working. Sometimes, this would fail, particularly if the computer was under heavy load. We now have each thread sleep for a different amount of time before attemping the lock. The result is that the lock gets hit consistently.
Ran the tests a couple dozen times. Couldn't reproduce the failure. I was
able to hit it more consistently than that before.