Print warning, skip test if paho-mqtt not available.

test/broker/03-publish-qos1-queued-bytes.py

@@ -9,8 +9,12 @@ import socket
 import threading
 import time
 
-import paho.mqtt.client
-import paho.mqtt.publish
+try:
+    import paho.mqtt.client
+    import paho.mqtt.publish
+except ImportError:
+    print("WARNING: paho.mqtt module not available, skipping byte count test.")
+    exit(0)
 
 
 import inspect, os, sys