[Docs] Expected Backups in OpenStack-Ansible

[Damian Cikowski]

This bug tracker is for errors with the documentation, use the following as a template and remove or add fields as you see fit. Convert [ ] into [x] to check boxes:

- [x] This doc is inaccurate in this way: MySQL data IS NOT automatically backed up. There is a bind mount for /var/backup in Galera container but no backup scripts nor schedule exist.
- [ ] This is a doc addition request.
- [ ] I have a fix to the document that I can paste below including example: input and output.

If you have a troubleshooting or support issue, use the following resources:

 - Ask OpenStack: http://ask.openstack.org
 - The mailing list: http://lists.openstack.org
 - IRC: 'openstack' channel on Freenode

-----------------------------------
Release: 16.0.6.dev26 on 2018-01-12 22:45
SHA: 52d09915237d1931c834e6c402eb4212391be3d5
Source: https://git.openstack.org/cgit/openstack/openstack-ansible/tree/doc/source/admin/maintenance-tasks/backups.rst
URL: https://docs.openstack.org/openstack-ansible/pike/admin/maintenance-tasks/backups.html

[Dmitriy Rabotyagov (noonedeadpunk)]

Mariadb backuprs are implemented with https://review.opendev.org/c/openstack/openstack-ansible-galera_server/+/755261