Mqtt hostname and port should be configurable

[mikehaller]

The self update agent currently uses static configuration "mosquitto:1883" to connect to an MQTT broker.
The URL to connect to should be configurable (command line arguments and/or environment variables).

Please also note that there is MQTTS and Authentication options, which should also be supported in the future.

[tobiwan3]

Issue is accepted and will be planned in 3 steps

1. --host and --port command line parameters are prepared in an implementation and are planned to be merged in the next 1-2 weeks.
2. Support will be switched to providing a url via either command line or environment variables
3. Adding support for MQTTS and authentication

[OleksandrChaika]

@mikehaller
Configurable MQTT server address is available in form tcp://host:port in version build-26 and newer.