code: func discoverErr(format string, a ...interface{}) error {
  	var s string
  	if len(a) > 1 {
  		s = fmt.Sprintf(format, a...)
  	} else {
  		s = format
  	}
  	return fmt.Errorf("discover-vsphere: %s", s)
  }
docs: // discoverErr prints out a friendly error heading for the top-level discovery
  // errors. It should only be used in the Addrs method.