libmachine/drivers/rpc/client_driver.go
func (c *RPCClientDriver) rpcStringCall(method string) (string, error) {
	var info string

	if err := c.Client.Call(method, struct{}{}, &info); err != nil {
		return "", err
	}

	return info, nil
}
func (c *RPCClientDriver) rpcStringCall(method string) (string, error) {
	var info string

	if err := c.Client.Call(method, struct{}{}, &info); err != nil {
		return "", err
	}

	return info, nil
}
// Helper method to make requests which take no arguments and return simply a
// string, e.g. "GetIP".