Make GC timeout configurable

workers/gcworker.py

@@ -9,7 +9,8 @@ logger = logging.getLogger(__name__)
 class GarbageCollectionWorker(Worker):
   def __init__(self):
     super(GarbageCollectionWorker, self).__init__()
-    self.add_operation(self._garbage_collection_repos, 30)
+    self.add_operation(self._garbage_collection_repos,
+                       app.config.get('GARBAGE_COLLECTION_FREQUENCY', 30))
 
   def _garbage_collection_repos(self):
     """ Performs garbage collection on repositories. """