registry.new() support the log function as argument

[prune998]

now you can call
hub, err := registry.New(*registryURL, *username, *password, log.Infof)
so all the logs will go through your favorit logger, like logrus.
Ex code :

func main() {
	log.Out = os.Stdout
	log.Formatter = new(logrus.JSONFormatter)
	log.Level = logrus.DebugLevel

	flag.Parse()
	hub, err := registry.New(*registryURL, *username, *password, log.Infof)
	if err != nil {
		log.Fatalf("error connecting to hub, %v", err)
	}
...

Ypu can switch log.Level = logrus.DebugLevel to log.Level = logrus.WarnLevel to disable logging