Block until all reservations are received.

def await_reservations(self, sc, status={}, timeout=600):
    """Block until all reservations are received."""
    timespent = 0
    while not self.reservations.done():
      logging.info("waiting for {0} reservations".format(self.reservations.remaining()))
      # check status flags for any errors
      if 'error' in status:
        sc.cancelAllJobs()
        sc.stop()
        sys.exit(1)
      time.sleep(1)
      timespent += 1
      if (timespent > timeout):
        raise Exception("timed out waiting for reservations to complete")
    logging.info("all reservations completed")
    return self.reservations.get()