Ensure net.ipv6.conf.lo.disable_ipv6=0
Ensure net.ipv6.conf.lo.disable_ipv6=0

Along the same lines as https://review.opendev.org/#/c/580460/.

Currently, the Erlang Port Mapper Daemon requires that the loopback
interface supports IPv6 in order to initialize properly.
Without that, rabbitmq-server cannot start and deployment fails at step 2.

Until the startup behaviour of epmd is amended, do not disable inet6 support
on loopback device to workaround the problem.

Change-Id: Ia747103aca99f3f45d7705248c6c1ef19aa93d71

openstack/tripleo-heat-templates,openstack/tripleo-heat-templates