vm-hosts: Add missing kube.network config

When I added the *systemd-networkd* configuration for the Kubernetes
network interface on the VM hosts, I only added the `.netdev`
configuration and forgot the `.network` part.  Without the latter,
*systemd-networkd* creates the interface, but does not configure or
activate it, so it is not able to handle traffic for the VMs attached to
the bridge.

group_vars/vm-hosts.yml

@@ -179,6 +179,13 @@ vmhost_networks:
     Description: pyrocufflink.blue VM network bridge
     DHCP: 'no'
     LinkLocalAddressing: 'no'
+- name: 60-kube
+  Match:
+    Name: kube
+  Network:
+    Description: Kubernetes network bridge
+    DHCP: 'no'
+    LinkLocalAddressing: 'no'
 - name: 60-mgmt
   Match:
     Name: mgmt