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

overcloud.j2.yaml

@@ -373,7 +373,13 @@ resources:
       EnabledServices: {get_attr: [{{role.name}}ServiceNames, value]}
       ServiceNetMap: {get_attr: [ServiceNetMap, service_net_map_lower]}
       ServiceHostnameList: {get_attr: [{{role.name}}, hostname]}
-      NetworkHostnameMap:
+      NetworkHostnameMap: {get_attr: [{{role.name}}NetworkHostnameMap, value]}
+
+  {{role.name}}NetworkHostnameMap:
+    type: OS::Heat::Value
+    properties:
+      type: json
+      value:
         # Note (shardy) this somewhat complex yaql may be replaced
         # with a map_deep_merge function in ocata.  It merges the
         # list of maps, but appends to colliding lists so we can
@@ -740,4 +746,10 @@ outputs:
     value:
 {% for role in roles %}
       {{role.name}}: {get_attr: [{{role.name}}IpListMap, net_ip_map]}
+{% endfor %}
+  RoleNetHostnameMap:
+    description: Mapping of each network to a list of hostnames for each role
+    value:
+{% for role in roles %}
+      {{role.name}}: {get_attr: [{{role.name}}NetworkHostnameMap, value]}
 {% endfor %}