avoid useless stacktraces in celery log

src/c3nav/mapdata/tasks.py

@@ -1,5 +1,6 @@
 import logging
 
+from celery.exceptions import MaxRetriesExceededError
 from django.db import DatabaseError
 from django.utils.formats import date_format
 from django.utils.translation import ugettext_lazy as _
@@ -18,6 +19,7 @@ def process_map_updates(self):
         logger.info('Processing map updates...')
 
     from c3nav.mapdata.models import MapUpdate
+    try:
         try:
             updates = MapUpdate.process_updates()
         except DatabaseError:
@@ -25,6 +27,9 @@ def process_map_updates(self):
                 raise
             logger.info('Processing is already running, retrying in 30 seconds.')
             raise self.retry(countdown=30)
+    except MaxRetriesExceededError:
+        logger.info('Cannot retry, retries exceeded. Exiting.')
+        return
 
     if updates:
         print()