Exposes the Glance registry_host Parameter

Previously, the registry_host parameter was not exposed to the
openstack::controller class.  This prevented the class from
managing the parameter.

The new parameter glance_registry_host was added to allow users
to manage the IP address used by the Glance API service for
communicating with the Glance Registry service.

Defaults to '0.0.0.0' for backwards compatibility.

Change-Id: Ica07c59ab6ad02a825f67abd6bde5f1043993ac3
Merge "Exposes the Glance registry_host Parameter"