Use specific role for backup add-ons

home-assistant/supervisor#755

Author: tjorim

remote-backup/config.json

@@ -7,7 +7,7 @@
   "startup": "once",
   "boot": "manual",
   "hassio_api": true,
-  "hassio_role": "manager",
+  "hassio_role": "backup",
   "map": ["backup:rw"],
   "options": {
     "ssh_host": "",