Move security notification work into its own method to allow for return values

Fixes #1302
Fixes #1304

workers/security_notification_worker.py

@@ -15,6 +15,14 @@ _LAYER_LIMIT = 100 # The number of layers to request on each page.
 
 class SecurityNotificationWorker(QueueWorker):
   def process_queue_item(self, data):
+    self.perform_notification_work(data)
+
+  def perform_notification_work(self, data):
+    """ Performs the work for handling a security notification as referenced by the given data
+        object. Returns True on successful handling, False on non-retryable failure and raises
+        a JobException on retryable failure.
+    """
+
     notification_name = data['Name']
     current_page = data.get('page', None)