OpenStack: add dhcp-duid to NetworkManager config

Adding ipv6.dhcp-duid=ll means we get a predictable client ID so that
reservations can be made on the DHCP server - this is useful if you
want to provide the hostname via DHCP (although a reverse DNS lookup
should also work)

Reservations are also required to ensure the controlplane IP of the
masters won't ever change post-deployment which will be necessary if
the DNS lookup approach is taken to set the hostnames.

This ports the BM fix from
openshift#1395 to
OpenStack platform.

templates/common/openstack/files/openstack-NetworkManager-conf.yaml

@@ -6,3 +6,5 @@ contents:
     [main]
     dhcp=dhclient
     rc-manager=unmanaged
+    [connection]
+    ipv6.dhcp-duid=ll