Database product recognition fails when the Hibernate "connection.driver_class" property is not set

Right now we try to recognize the DB product using the Hibernate "connection.driver_class" property when there's no Session Factory. However this has two downsides:
1. When there are new drivers, then we fail to recognize the DB. For example MySQL added "com.mysql.cj.jdbc.Driver" (in addition to "com.mysql.jdbc.Driver"), see XWIKI-17380
1. Some JDBC drivers are registered automatically using the Service Loader mechanism and thus don't need a Hibernate "connection.driver_class" property to be set. Thus if our user don't see that property we won't recognize the DB product.