Merge branch 'mariadb' into 'master'

Mariadb

See merge request hpc-team/ansible_cluster_in_a_box!234

Former-commit-id: 16451abd

roles/slurmdb-config/readme.md

+If the database is already up and running, running this role will not work.
+To make a change to the log file size without data loss before applying the config.
+
+1. While mariadb is still runing 
+   MySQL> SET GLOBAL innodb_fast_shutdown=0;
+2. Stop mariadb
+   systemctl stop mariadb
+3. Run this role to copy the config to /etc/my.cnf.d
+4. Go to /var/lib/mysql
+   mv ib_logfile0 ib_logfile0_orig
+   mv ib_logfile1 ib_logfile1_orig
+5. systemctl start mariadb