[Feature] Move datadir after install (issue #25)

When ``node['mariadb']['mysqld']['datadir']`` is different than the default ``/var/lib/mysql``, this will trigger after install a script that stop the service, moves the datadir to its new location, replace it with a symlink to the new path and restart the service. Tested on Ubuntu 14.04 with MariaDB 10.0
In fact here, you need to stop the mysql service, and restart it just after (you can have 3 notifies lines) It's really better.