Clarify comment about binding erlang to IPv4

The comment was confusing and not explaining what the real issue is
when binding erlang to an IPv4 address.

Change-Id: I819ea137fa37c0b2711efb1e7cb1e518ae26b9ab
Related-Bug: #1562701

ansible/roles/rabbitmq/templates/rabbitmq-env.conf.j2

@@ -4,11 +4,15 @@ RABBITMQ_BOOT_MODULE=rabbit_clusterer
 RABBITMQ_LOG_BASE=/var/log/kolla/rabbitmq
 RABBITMQ_SERVER_ADDITIONAL_ERL_ARGS="-pa /usr/lib/rabbitmq/lib/rabbitmq_server-3.5.7/plugins/rabbitmq_clusterer-3.5.x-189b3a81.ez/rabbitmq_clusterer-3.5.x-189b3a81/ebin"
 
-# TODO(sdake, vhosakot) Heisenbugs await if the control services are collocated on
-# one node.  The reason is epmd binds to wildcard (all interfaces) and could
-# potentially interact with the neutron external or tenant networks.
-# unfortunately epmd is broken with ipv6, so yeah, no bueno.
-# See bug https://bugs.launchpad.net/ubuntu/+source/erlang/+bug/1374109
+# TODO(sdake, vhosakot)
+# erlang by default binds to wildcard (all interfaces) and can potentially
+# interfere with the neutron external or tenant networks. We should in theory
+# bind epmd to the host's IPv4 address to address the issue however this also
+# has issues and can crash erlang when it is compiled with IPv6 support.
+# See bugs:
+# https://bugs.launchpad.net/ubuntu/+source/erlang/+bug/1374109
+# https://bugs.launchpad.net/kolla/+bug/1562701
+# https://bugzilla.redhat.com/show_bug.cgi?id=1324922
 # export ERL_EPMD_ADDRESS={{ hostvars[inventory_hostname]['ansible_' + api_interface]['ipv4']['address'] }}
 
 export ERL_EPMD_PORT={{ rabbitmq_epmd_port }}