Add RoleNetHostnameMap output
Add RoleNetHostnameMap output

This exposes a list of hostnames similar to the RoleNetIpMap, this
will be consumed by the dynamic inventory ref
https://review.openstack.org/465558

Change-Id: I61efac5634e9b6fbb820e693c71a0adae5fa8b6a

openstack/tripleo-heat-templates,openstack/tripleo-heat-templates,dprince/tripleo-heat-templates,dprince/tripleo-heat-templates