message: Use explicit exit code when shutting down a cluster.
diff: @@ -145,14 +145,13 @@ class WorkerHeartbeatManager(object):
  # Default timeout is set to allow other shutdown triggered operations (log
  # flushing etc) to finish before terminating the worker.
  - def shutdown(self, wait_time_in_ms=60000, exit_code=None):
  + def shutdown(self, wait_time_in_ms=60000, exit_code=0):
  """Shutdown all workers after `shutdown_timeout_secs`."""
  logging.info('Shutting down %s.', self)
  req = event_pb2.WorkerHeartbeatRequest(
  watchdog_config=event_pb2.WatchdogConfig(timeout_ms=wait_time_in_ms),
  shutdown_mode=event_pb2.SHUTDOWN_AFTER_TIMEOUT,
  - exit_code=event_pb2.RequestedExitCode(
  - exit_code=exit_code) if exit_code is not None else None)
  + exit_code=event_pb2.RequestedExitCode(exit_code=exit_code))
  self.configure(req)
  # Wait for workers to shutdown.
  @@ -198,7 +197,7 @@ class WatchdogManager(threading.Thread):
  session,
  devices=None,
  ping_interval=60,
  - shutdown_timeout=3600):
  + shutdown_timeout=2 * 3600):
  """Initialize a watchdog manager.
  Args:
  