Add some requires to the module so that we ensure the
exim package is installed before configuring the etc config
file and starting the service.
Change-Id: I5c464a9b8b6ecbdea7af3a4b9bdf344f3a40c0db
Reviewed-on: https://review.openstack.org/23552
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins