[Rdo-list] Packstack Juno with existing external network?

Hi, Setup: workstation with F20 + libvirt/kvm (nested virt enabled) and several VMs like MariaDB Galera cluster VMs, HAProxy VMs, OpenLDAP cluster VMs, RabbitMQ cluster VMs etc. Each VM gets assigned an IP address via DHCP in the 10.0.0.0/24 range. Goal: packstack to create 1 Controller node and 2 Compute nodes (Juno) on 3 freshly provisioned CentOS 7 VMs. The Cirros instance on any of the 2 Compute nodes should have Internet access and it should be possible to access the Cirros instance on its floating IP from the local 10.0.0.0/24 network. I just read: https://openstack.redhat.com/Neutron_with_existing_external_network and was wondering if there is a way I can get that setup pre-defined in a packstack answer file? If yes, any suggestions which vars need to be defined? Thanks, Patrick