Update config templates for Juno release

This is the updated https://github.com/crowbar/barclamp-nova_dashboard/pull/196
AFAIK there's not way to disable IPv6 completely in Neutron. In Juno the support of IPv6 is not so bad, see http://techs.enovance.com/7199/journey-of-ipv6-in-openstack (it's a nice post)