Change xtrabackup to mariadb-backup for mariadb 10.3

xtrabackup doesnt work with mariadb 10.3,
need to be changed to mariadb-backup tool.

For now only migrate galera, not kolla-backup tool
to fix the CI.

https://jira.mariadb.org/browse/MDEV-15774

Change-Id: Ie77ae41e419873feed4b036a307887b22455183b
Depends-On: Icefe3a77fb12d57c869521000d458e3f58435374

ansible/roles/mariadb/templates/galera.cnf.j2

 {%- set wsrep_driver = '/usr/lib/galera/libgalera_smm.so' if kolla_base_distro in ['debian', 'ubuntu'] else '/usr/lib64/galera/libgalera_smm.so' %}
-{% set sst_method = 'mariabackup' if kolla_base_distro in ['debian'] else 'xtrabackup-v2' %}
+{% set sst_method = 'mariabackup' %}
 
 [client]
 default-character-set=utf8