libmachine/drivers/serial.go
func (d *SerialDriver) GetURL() (string, error) {
	d.Lock()
	defer d.Unlock()
	return d.Driver.GetURL()
}
func (d *SerialDriver) GetURL() (string, error) {
	d.Lock()
	defer d.Unlock()
	return d.Driver.GetURL()
}
// GetURL returns a Docker compatible host URL for connecting to this host
// e.g. tcp://1.2.3.4:2376