swift: use ipv6 binding on centos7 nodes
swift: use ipv6 binding on centos7 nodes

If IPv6 is enabled (on centos7 now), deploy Swift using this binding.
Note: adding notes in TODO to also deploy memcached in IPv6 later.

Change-Id: I8c8e8e8870212765f8b8a0d639194e040963d6e0

openstack/puppet-openstack-integration,openstack/puppet-openstack-integration,openstack/puppet-openstack-integration