Currently all services are setup in the haproxy configuration,
even if there are no back-ends for it.
This patch implements the use of the service enablement by
validating whether the service is in the inventory.
Additional checks are done for glance-registry to validate
whether it's needed.
Change-Id: Ie192cbe3b24573063aff93e9acfcefa92030504f
Closes-Bug: #1742717