tests: repair --random_activity_priority argument

This stopped working when the signature of Message.__init__ changed in
06aee0c2 (CMFActivity.ActivityTool: Use uid for identity check instead of
oid., 2019-09-17)

product/ERP5Type/tests/ERP5TypeTestCase.py

@@ -1622,10 +1622,10 @@ def fortify():
     rng = random.Random(seed)
     from Products.CMFActivity.ActivityTool import Message
     Message__init__ = Message.__init__
-    def __init__(self, url, oid, active_process, active_process_uid,
+    def __init__(self, url, document_uid, active_process, active_process_uid,
                  activity_kw, *args, **kw):
       activity_kw['priority'] = rng.randint(-128, 127)
-      Message__init__(self, url, oid, active_process, active_process_uid,
+      Message__init__(self, url, document_uid, active_process, active_process_uid,
                       activity_kw, *args, **kw)
     Message.__init__ = __init__