getDatabaseProductName() return DatabaseProduct.UNKNOWN for MariaDB depending on the configuration

A workaround is to add "useMysqlMetadata=true" in the jdbc URL. Another possibility is to use the mysql connector which works fine with MariaDB.

Since MySQL and MariaDB are the same thing from XWiki point of view (for now at least) we should return DatabaseProduct.MySQL for now so that it covers any existing code which have a if on MySQL.