DF/091: bug fix (incorrect submodule name).

The bug appeared due to the merge of two too long-living branches:
* the submodule was moved in the `pyDKB` branch (5e3003e), and
* used for the second time in `master` (a0226ff).

It tells us, by the way, that the better idea would be to import this
module in the beginning, as long as it is used more than one time...

Utils/Dataflow/091_datasetsRucio/datasets_processing.py

@@ -154,7 +154,7 @@ def process_input_ds(stage, message):
         except RucioException:
             data[mfields['bytes']] = -1
             data[mfields['deleted']] = True
-    stage.output(pyDKB.dataflow.messages.JSONMessage(data))
+    stage.output(pyDKB.dataflow.communication.messages.JSONMessage(data))
 
     return True