Werk #15897: mk_mysql: Make Checkmk the sole provider of mysql configuration

Currently, the configuration used to access mysql when using the mk_mysql agent plugin can come from different sources, depending on what option files exist on the remote server. This means that a configuration provided by the agent rule "MySQL Databases" can be overridden by an existing option file that comes first in the file processing order.

This werk changes this to explicitly use the Checkmk configuration in $MK_CONFDIR/mysql.cfg.

If you have been using other configuration files, you will need to set up your access in the "MySQL Databases" rule.

To the list of all Werks