message: Fix a typo in coordinator_test.py. threads[1:1] is the empty array, so we were't
  actually waiting for threads[1].
diff: @@ -133,7 +133,7 @@ class CoordinatorTest(test.TestCase):
  t.start()
  WaitForThreadsToRegister(coord, 2)
  # threads[1] is not registered we must pass it in.
  - coord.join(threads[1:1])
  + coord.join([threads[1]])
  for t in threads:
  self.assertFalse(t.is_alive())
  