Set a timeout on the lock acquisition

Occasionally, status.rst hangs. This is an attempt to at least avoid such hangs by timing out on the lock acquisition. It's the only thing in this test that I can see would cause such a hang, but the problem is so intermittent that it's very difficult to debug (and never happens in local tests).

If this is the problem, it means the master lock was acquired before we got here, so the test should have failed in first command() call. But we would never see that because doctests don't have a trace functionality afaict.

It's all I can think of though.