Use hostvars to get ansible_default_ipv6
Use hostvars to get ansible_default_ipv6

I think this is missing picking this up from hostvars, so always
assumes ipv4.

Change-Id: I65929a87f864701ac07966a6b0d9ca9225da5145

openstack-infra/openstack-zuul-jobs,openstack-infra/openstack-zuul-jobs