code: func convertExtraHostsToSwarmHosts(extraHosts []string) []string {
  	hosts := []string{}
  	for _, extraHost := range extraHosts {
  		parts := strings.SplitN(extraHost, ":", 2)
  		hosts = append(hosts, fmt.Sprintf("%s %s", parts[1], parts[0]))
  	}
  	return hosts
  }
docs: // convertExtraHostsToSwarmHosts converts an array of extra hosts in cli
  //     <host>:<ip>
  // into a swarmkit host format:
  //     IP_address canonical_hostname [aliases...]
  // This assumes input value (<host>:<ip>) has already been validated