Pin mosquitto to 1.6.14

Mosquitto 2.0 adds a breaking change where port will be bound to the
loopback device. This makes integration with docker difficult (requiring
an additional config file).  Since this is on a private network, we'll
just resolve by pinning to an older reelase.

docker-compose.yml

@@ -235,7 +235,7 @@ services:
     volumes:
     - /etc/localtime:/etc/localtime:ro
   mqtt:
-    image: eclipse-mosquitto
+    image: eclipse-mosquitto:1.6.14
     container_name: mqtt
     restart: always
     ports: