mariadb: enable galera clustering by default
mariadb: enable galera clustering by default

Kolla assumes mariadb 10.0 where galera stuff was always enabled. And
this works for CentOS and Ubuntu as they use 10.0 on x86-64.

Debian uses mariadb 10.1 by default (and CentOS on !x86-64 and
Ubuntu/aarch64) where galera stuff is disabled by default.

Closes-Bug: 1740060
Co-Authored-By: Xinliang Liu <ccbb14b249507ad70d61bb79d1081624f81810a9@linaro.org>
Change-Id: I8374ac2219ad7880970cd789727d01af7cac1077

dardelean/kolla-ansible,dardelean/kolla-ansible,dardelean/kolla-ansible