See http://download1.parallels.com/Plesk/PP12/plesk-12.5-for-linux-change-log.html
[-] On CentOS 7 x64 servers, after installing MariaDB version 10 or 10.1 the MySQL component was marked as “not installed” in the Plesk Installer. (PPP-18000)
So i was confused, if MariaDB 10.1 is supported or not.