[AIRFLOW-682] Bump MAX_PERIODS to make mark_success work for large DAGs

It is not possible to mark success on some large
DAGs due to the MAX_PERIODS being set to 1000. We
should temporarily bump it up until work can be
done to scale the mark success endpoint much
higher.

Testing Done:
- Has been running in Airbnb prod for many months
now

Closes apache#1928 from aoen/ddavydov/bump_max_periods

airflow/www/views.py

@@ -1095,7 +1095,7 @@ def success(self):
         future = request.args.get('future') == "true"
         past = request.args.get('past') == "true"
         recursive = request.args.get('recursive') == "true"
-        MAX_PERIODS = 1000
+        MAX_PERIODS = 5000
 
         # Flagging tasks as successful
         session = settings.Session()