This allows aodh service endpoints to use custom hostnames, and adds the
following variables:

* aodh_internal_fqdn
* aodh_external_fqdn

These default to the old values of kolla_internal_fqdn or
kolla_external_fqdn.

This also adds a aodh_api_listen_port option, which defaults to
aodh_api_port for backward compatibility.

This option allow the user to differentiate between the port the
service listens on, and the port the service is reachable on. This is
useful for external load balancers which live on the same host as the
service itself.

Change-Id: Iee08b725d066bfbe543d9319c47941d59c22212a
Implements: blueprint service-hostnames