Use dynamic client id for controller

controller-host/mqttthread.lua

@@ -46,14 +46,17 @@ end
 local function main()
 	client = mqtt.client {
 		uri = "mqtt.seeseepuff.be",
-		username = "mqtt_controller",
+		username = "mqtt_controller-" .. math.random(0, 999999999),
 		clean = true,
 		reconnect = 5,
 	}
 
 	client:on {
 		connect = onConnect,
-		message = onMessage
+		message = onMessage,
+		error = function(message)
+			print("MQTT error: " .. message)
+		end
 	}
 
 	print("Connecting")