Use ipv6 resolvers only with ipv6 networking
Use ipv6 resolvers only with ipv6 networking

If we have ipv6 networking that is routable then only use ipv6 name
resolvers to avoid traversing potential NAT with ipv4. If we don't have
ipv6 available and routable then only use ipv4 resolvers to avoid
timeouts and failovers.

Change-Id: I885418e07265002b09592c3cf3aff9712c6e001f

openstack-infra/project-config,openstack-infra/project-config