Small improvement on the trigger/views filtering in the database dump

In provision/db/mysql/mysql_service.inc, there is a 'sed' on some MySQL data which can cause problems when migrating a site with views/triggers.

Attached a tiny patch to make that sed more tolerant to various MySQL versions.

i.e. my sqldump had:

/*!50017 DEFINER=`example`@`localhost`*/

And the sed regexp expected a space after the hostname:

/*!50017 DEFINER=`example`@`localhost` */

Noticed this on a MySQL server running 5.1.49-3~bpo50+1.