TMSS-190: added option to override DEAULT_BUSNAME via environment

LCS/Messaging/python/messaging/config.py

@@ -61,4 +61,4 @@ for port in possible_ports:
                      DEFAULT_BROKER, port, DEFAULT_USER, e)
 
 # default exchange to use for publishing messages
-DEFAULT_BUSNAME = adaptNameToEnvironment("lofar")
+DEFAULT_BUSNAME = os.environ.get('LOFAR_DEFAULT_BUSNAME', adaptNameToEnvironment("lofar"))