MySQLnd and PHP 5.5

With newer versions of MySQL (MariaDB in particular), you'll get client
lib/server header mismatch warnings. Replacing php-mysql with the
php-mysqlnd module (nd = native driver) fixes this.

There were also problems with the MariaDB installation script which
didn't sort out iptables or add the service. I've added those and tested
by deleting and reprovisioning, and that now works fine.