Add support for the default_dns_nameservers variable

This variable was introduced in Newton and allows you to specify a
list of default DNS servers populated when creating a tenant subnet.

Change-Id: I7c6767bb883296c55b7a7302d7af8a8721fd2844

defaults/main.yml

@@ -128,6 +128,9 @@ horizon_simple_ip_management: True
 # To enable ha router support in horizon set to True
 horizon_enable_ha_router: False
 
+# Provide default DNS servers to use when a subnet is created.
+horizon_default_dns_nameservers: []
+
 # DISALLOW_IFRAME_EMBED can be used to prevent Horizon from being embedded
 # within an iframe. Legacy browsers are still vulnerable to a Cross-Frame
 # Scripting (XFS) vulnerability, so this option allows extra security hardening

templates/horizon_local_settings.py.j2

@@ -315,7 +315,18 @@ OPENSTACK_NEUTRON_NETWORK = {
     # port.
     # VNIC types include 'normal', 'macvtap' and 'direct'.
     # Set to empty list or None to disable VNIC type selection.
-    'supported_vnic_types': ['*']
+    'supported_vnic_types': ['*'],
+
+    {% if horizon_default_dns_nameservers is defined %}
+    # Default DNS servers you would like to use when a subnet is created.
+    # This is only a default. Users can still choose a different list of
+    # dns servers.
+    'default_dns_nameservers': [
+      {% for item in horizon_default_dns_nameservers %}
+        '{{ item }}',
+      {% endfor %}
+    ]
+    {% endif %}
 }
 
 # The OPENSTACK_HEAT_STACK settings can be used to disable password