disable automatic root password (#26)
- The variables `mariadb_root_home`, `mariadb_root_username`, `mariadb_root_password` and
`mariadb_root_password_update` have been removed and replaced by the dictionary `mariadb_system_users`.
- add CHANGELOG
- The setting of the root password can be prevented
- The filter `system_user` has been added and can separate a user from the dictionary `mariadb_system_users`.
- `mariadb_monitoring` must now be explicitly activated
- `mariadb_mysqltuner` must now be explicitly activated
Full Changelog: 2.5.3...2.6.0