Fix purging unattended-upgrades in template generator

Change-Id: Idbf7bdc4237eaab36cf2bfebb5c5105378775875
diff --git a/tcp_tests/templates/cookied-model-generator/underlay.yaml b/tcp_tests/templates/cookied-model-generator/underlay.yaml
index 25fb76c..4783bd8 100644
--- a/tcp_tests/templates/cookied-model-generator/underlay.yaml
+++ b/tcp_tests/templates/cookied-model-generator/underlay.yaml
@@ -29,6 +29,16 @@
           ip_ranges:
             dhcp: [+90, -10]
 
+      external-pool01:
+        net: {{ os_env('ADMIN_ADDRESS_POOL01', '10.90.0.0/16:24') }}
+        params:
+          ip_reserved:
+            gateway: +1
+            l2_network_device: +1
+            default_{{ HOSTNAME_CFG01 }}: +15
+          ip_ranges:
+            dhcp: [+90, -10]
+
     groups:
       - name: default
         driver:
@@ -46,11 +56,17 @@
           admin: admin-pool01
 
         l2_network_devices:
+          external:
+            address_pool: external-pool01
+            dhcp: true
+            forward:
+              mode: nat
+
           admin:
             address_pool: admin-pool01
             dhcp: true
             forward:
-              mode: nat
+              mode: route
 
         nodes:
           - name: {{ HOSTNAME_CFG01 }}
@@ -78,9 +94,15 @@
 
               interfaces:
                 - label: ens3
+                  l2_network_device: external
+                  interface_model: *interface_model
+                - label: ens4
                   l2_network_device: admin
                   interface_model: *interface_model
               network_config:
                 ens3:
                   networks:
+                    - external
+                ens4:
+                  networks:
                     - admin