vm: fix save_as

https://git.ik.bme.hu/circle/cloud/snippets/34

circle/vm/operations.py

@@ -336,6 +336,7 @@ class SaveAsTemplateOperation(InstanceOperation):
             'system': self.instance.system,
             'system': self.instance.system,
         }
         }
         params.update(kwargs)
         params.update(kwargs)
+        params.pop("parent_activity", None)
 
 
         from storage.models import Disk
         from storage.models import Disk