Retrieve the URL of the broker to which an MQTT client is connected
String — The URL of the MQTT broker
This method allows you to retrieve the URL of the MQTT broker to which the mqttclient object is connected and was provided when the connection attempt was made (ie. by using the imp API method mqttclient.connect()).
The call returns a string which will be prefixed
tcp:// for unencrypted connections, or
ssl:// for encrypted connections.