MQTT event loop optimization and added support for Unix Domain Sockets for MQTT communication

[florinmihut]

• Added support for Unix Domain Sockets for MQTT communication
  • Created a new config option 'mqtt_broker_socket_path' where one can provide the socket path
  • The config option mutual exclusive to the normal TCP socket and will raise an exception if both are provided in the config file (or as env variable)
  • There is no default value for the UDS path, it must be provided in the config file
  • We keep the backward compatibility, thus if nothing is provided in the config file, the default MQTT values are used (localhost:1883)
  • Beside functionality added, this provides an optimization over the TCP connection (observed on slow systems around 5%)
  • Updated the config schema to for the new option
• Optimization made in the MQTT event loop (we moved from executing the event loop from 100ms to 300s)
  • Normally the keep alive message is send by the MQTT lib, in certain cases however this might not work unless you call mqtt_sync often and on regular basis (few ms)
  • We decreased the event loop execution frequency drastically (on slow systems we can see a decrease of CPU usage around 10%)

[florinmihut]

Looks to me that Codacy has some false positives, I tried to "fix" them to make it see that is a false positive but in vain.