code: func (d *Driver) getCloudInit() ([]byte, error) {
  	var err error
  	if d.UserDataFile != "" {
  		d.UserData, err = ioutil.ReadFile(d.UserDataFile)
  	}
  
  	return d.UserData, err
  }
docs: // Build a cloud-init user data string that will install and run
  // docker.