[RFE] Add support for Munin plugins to Percona-monitoring-plugins

Munin[1] is a widely used alternative to Cacti, supporting a robust plugin architecture[2], while also offering a basic level of alerting.

The existing mysql plugin[3] already does a great job of monitoring base MySQL checks (including SHOW INNODB STATUS), but does not currently take into consideration any Percona-specific metrics (though notably, it *does* do galera specific checks for MariaDB). It'd be great to see Percona take up maintenance of the mysql plugin and update it to work with these advanced metrics.

Thanks!

[1] http://munin-monitoring.org
[2] http://munin-monitoring.org/wiki/plugins
[3] https://github.com/munin-monitoring/munin/blob/devel/plugins/node.d/mysql_.in