Quota shows warnings on backup creation

Logs show deprecation warning in the logs when creating backups.

Warnings are related to the "backups" and "backup_gigabytes" quota resources:

  Nov 26 10:03:32 localhost.localdomain <email address hidden>[390423]: WARNING cinder.quota [req-e3682860-e795-4db7-99ce-841b59479a2b req-673716ec-5706-43c2-bc02-ac95f6c1f18c admin admin] Deprecated: Default quota for resource: backups is set by the default quota flag: quota_backups, it is now deprecated. Please use the default quota class for default quota.

  Nov 26 10:03:32 localhost.localdomain <email address hidden>[390423]: WARNING cinder.quota [req-e3682860-e795-4db7-99ce-841b59479a2b req-673716ec-5706-43c2-bc02-ac95f6c1f18c admin admin] Deprecated: Default quota for resource: backup_gigabytes is set by the default quota flag: quota_backup_gigabytes, it is now deprecated. Please use the default quota class for default quota.

This warning is shown because the ``quota_classes`` table doesn't have entries for these 2 resources for the "default" quota class, unlike the other quota resources (``volumes``, ``gigabytes``, ``snapshots``, etc.) which have them because they are added by the database migration.