bundles/backup-client: use set instead of list

bundles/backup-client/items.py

@@ -19,12 +19,12 @@ else:
 
 if node.metadata.get('backups/exclude_from_backups', False):
     # make sure nobody tries to do something funny
-    for file in [
+    for file in {
         '/etc/backup.priv',
         '/usr/local/bin/generate-backup',
         '/usr/local/bin/generate-backup-with-retries',
         '/var/tmp/backup.monitoring', # status file
-    ]:
+    }:
         files[file] = {
             'delete': True,
         }