Change external network subnet for data plane adoption hci

Adjust networking_mapper_definition_patch to create external network
as defined data-plane-adoption[1] and architectuere repo

[1]openstack-k8s-operators/data-plane-adoption#786

scenarios/adoption/hci.yml

@@ -59,7 +59,7 @@ libvirt_manager_patch_layout:
 networking_mapper_definition_patch:
   networks:
     external:
-      network: "172.21.0.0/24"
+      network: "10.0.0.0/24"
       vlan: 44
       mtu: 1496
   group-templates: