Fixed race condition in fetching task activities

Since MongoDB stores timestamps with a resolution of a millisecond, it was
possible for a task to be created and updated on the same timestamp, which
could cause an impossible ordering of the activities (edit before creation).
Sorting by ID instead of creation timestamp fixes this.

attract/__init__.py

@@ -218,7 +218,7 @@ class AttractExtension(PillarExtension):
                      'context_object': node_id},
                 ],
             },
-            'sort': [('_created', -1)],
+            'sort': [('_id', 1)],  # Sort by creation, _id is incremental.
             'max_results': max_results,
             'page': page,
         }, api=api)

attract/routes.py

@@ -51,7 +51,7 @@ def index():
         'where': {
             'project': {'$in': list(id_to_proj.keys())},
         },
-        'sort': [('_created', -1)],
+        'sort': [('_id', 1)],  # Sort by creation, _id is incremental.
         'max_results': 20,
     }, api=api)