Wait until the next action is needed.

def Wait(self):
    """Wait until the next action is needed."""
    time.sleep(self.sleep_time - int(self.sleep_time))

    # Split a long sleep interval into 1 second intervals so we can heartbeat.
    for _ in range(int(self.sleep_time)):
      time.sleep(1)

    # Back off slowly at first and fast if no answer.
    self.sleep_time = min(self.poll_max,
                          max(self.poll_min, self.sleep_time) * self.poll_slew)