code: func (d *Driver) Stop() error {
  	c, err := newComputeUtil(d)
  	if err != nil {
  		return err
  	}
  
  	if err := c.stopInstance(); err != nil {
  		return err
  	}
  
  	d.IPAddress = ""
  	return nil
  }
docs: // Stop stops an existing GCE instance.