Find an external network when no one is provided

Esternal network ID is stored in a Heat stack to keep the same network
ID for later test case executions.

Remove logic to found for looking for an external network from
DevStack plugin.

Change-Id: Ic7fe03324f4f328488988435530e127cedfab781

tobiko/openstack/stacks/neutron/floating_network.yaml

@@ -0,0 +1,40 @@
+heat_template_version: newton
+
+
+description: |
+  Creates an network with a subnet and a gateway router to an external network
+  if given
+
+
+parameters:
+  external_id:
+    description: Default value to be assigned to network ports
+    type: string
+    default: '<no-external-id>'
+
+  has_external_id:
+    description: Extra network creation parameters
+    type: boolean
+    default: false
+
+
+conditions:
+  has_network:
+    get_param: has_external_id
+
+
+resources:
+  network:
+    type: OS::Neutron::Net
+    external_id: {get_param: external_id}
+    condition: has_network
+
+
+outputs:
+  network_id:
+    description: Network ID
+    value: {get_resource: network}
+
+  has_network:
+    description: Whenever has a floating network
+    value: {get_param: has_external_id}

tobiko/openstack/stacks/neutron/network.yaml

@@ -75,9 +75,7 @@ parameters:
   gateway_network:
     description: Optional gateway network to route packages to
     type: string
-    default:
-    constraints:
-    - custom_constraint: neutron.network
+    default: '<no-gateway-network>'
 
   gateway_value_specs:
     description: Extra gateway router creation parameters