do not return movements with the same origin and target

xtreemfs_client/dataDistribution.py

@@ -318,6 +318,9 @@ class DataDistribution(object):
         new_assignments = self.add_folders(folders_to_be_reassigned)
 
         for folder_id, target in new_assignments:
+            if movements[folder_id] == target:
+                del movements[folder_id]
+            else:
                 movements[folder_id] = (movements[folder_id], target)
 
         return movements