Change exception to debug on expected RAC integrity error

Fixes https://jira.prod.coreos.systems/browse/QS-44

data/model/repositoryactioncount.py

@@ -63,7 +63,7 @@ def count_repository_actions(to_count):
     RepositoryActionCount.create(repository=to_count, date=yesterday, count=actions)
     return True
   except IntegrityError:
-    logger.exception('Exception when writing count for repository')
+    logger.debug('Count already written for repository %s', to_count.id)
     return False