Extends Nova Metadata Service Parameterization and Composition

Previously, nova enabled_apis was hard coded and metdata_host
was using PUBLIC_IP param instead of exposing an individual
param.

Extending these params and creating a separate compose yml that
includes compute/libvirt/network/api is required to support
nova network multi_host.

Additional details can be found here:

http://docs.openstack.org/admin-guide-cloud/content/section_metadata-service.html

Change-Id: I5d417a0ee460f8ad9b2982fe83d63ab57013918e