code: func (c *Conn) NodesShutdown(delay int, nodes ...string) error {
  	shutdownUrl := fmt.Sprintf("/_cluster/nodes/%s/_shutdown", strings.Join(nodes, ","))
  	if delay > 0 {
  		var values url.Values = url.Values{}
  		values.Add("delay", strconv.Itoa(delay))
  		shutdownUrl += "?" + values.Encode()
  	}
  	_, err := c.DoCommand("POST", shutdownUrl, nil, nil)
  	if err != nil {
  		return err
  	}
  	return nil
  }
docs: // NodesShutdown allows the caller to shutdown between one and all nodes in the cluster
  // delay is a integer representing number of seconds
  // passing "" or "_all" for the nodes parameter will shut down all nodes
  // see http://www.elasticsearch.org/guide/reference/api/admin-cluster-nodes-shutdown/