Fix exim depends.
Fix exim depends.

Handles "Could not perform immediate configuration on 'exim4-daemon-light'".

Change-Id: I49049071af2f5f323ef90485252d825351367522
Reviewed-on: https://review.openstack.org/353
Reviewed-by: James E. Blair <e81a02a9d6405977f63a769d9f6ec8ed9d924325@inaugust.com>
Tested-by: Jenkins

open-switch/infra_puppet-jenkins,open-switch/infra_puppet-jenkins