Add undercloud-networks-existing template

This file was missed in the original commit to add undercloud
network configuration templates. It's essentially a noop for adding
a second undercloud-like vm to the existing networks.

templates/undercloud-networks-existing.yaml

@@ -0,0 +1,44 @@
+heat_template_version: 2015-04-30
+
+parameters:
+  provision_net:
+    type: string
+    default: provision
+    description: Name of a network that will be used for provisioning traffic
+
+  provision_net_cidr:
+    type: string
+    description: CIDR for provision network subnet
+    default: 192.0.2.0/24
+
+  provision_net_shared:
+    type: boolean
+    description: Whether this network should be shared across all tenants
+    default: false
+
+  public_net:
+    type: string
+    description: Name of the overcloud external network
+    default: public
+
+  public_net_cidr:
+    type: string
+    description: CIDR for external network subnet
+    default: 10.0.0.0/24
+
+  public_net_shared:
+    type: boolean
+    description: Whether this network should be shared across all tenants
+    default: false
+
+
+outputs:
+  networks:
+    value:
+      provision: {get_param: provision_net}
+      public: {get_param: public_net}
+  # The provision and public network routers is here for compatibility only
+  provision_network_routers:
+    value: null
+  public_network_router:
+    value: null