[OS-4192] Fix crash when there are no queues in rabbit

src/sensor-rabbitmq.py

@@ -49,11 +49,14 @@ class Message(Metric):
             self.log(SENSOR_LOG_ERROR, str(e))
             return -1
 
-        data = json.loads(response)
-        messages = data['queue_totals']['messages']
+        try:
+            data = json.loads(response)
+            messages = data['queue_totals']['messages']
+        except KeyError as e:
+            # There are no messages
+            messages = 0
 
         self.storeSample01(messages)
-
         return 0
 
 class Partition(Metric):
@@ -145,4 +148,4 @@ class MessageRate(Metric):
 
         self.storeSample01(value)
 
-        return 0
\ No newline at end of file
+        return 0