Fix announcer test.

Testing Done:
The announcer test does not fail on my laptop.  But I predict what was
happening is that since I was just doing 2 clock.tick(1.0)s with the
ThreadedClock and the other end was doing a clock.sleep(2.0), there were no
guarantees that code was getting executed unless I did a subsequent
clock.tick(epsilon).  I've instead just done clock.tick(> 2) to guarantee
that code executes.

Bugs closed: AURORA-638

Reviewed at https://reviews.apache.org/r/24359/