install and configure mariadb on CentOS 7

variables:

mariadb_data_dir - default /var/lib/mysql
mariadb_user - default mysql
mariadb_root_password - lookup from group_names[0]}}/{{ inventory_hostname }}_mysql
mariadb_root_home - default /root
mariadb_root_username - default root
mariadb_backup_dir - directory where backups will be stored