Docs: update RabbitMQ HA instructions

``kolla-ansible genconfig`` includes some tasks [1] that require
containers to still be running. Move the config generation to be done
before containers are stopped.

Also make it clearer that containers should not be restarted with the
new config until after RabbitMQ state has been reset.

1. https://github.com/openstack/kolla-ansible/blob/master/ansible/roles/octavia/tasks/get_resources_info.yml#L2

Change-Id: I1d4fc32e5963a8e8fa4a8fc7c467cadf0f26fd5f
(cherry picked from commit 44aa76c)

Author: MoteHue

doc/source/reference/message-queues/rabbitmq.rst

@@ -134,18 +134,19 @@ additional steps needed to migrate from transient to durable queues.
    Bobcat release. This means that you will also need to perform this migration
    before a SLURP upgrade to Caracal.
 
-1. Stop all OpenStack services which use RabbitMQ, so that they will not
-   attempt to recreate any queues yet.
+1. Generate the new config for all services. After this, make sure not to
+   restart any containers until after the RabbitMQ state has been reset.
 
    .. code-block:: console
 
-      kolla-ansible stop --tags <service-tags>
+      kolla-ansible genconfig
 
-2. Generate the new config for all services.
+2. Stop all OpenStack services which use RabbitMQ, so that they will not
+   attempt to recreate any queues yet.
 
    .. code-block:: console
 
-      kolla-ansible genconfig
+      kolla-ansible stop --tags <service-tags>
 
 3. Reconfigure RabbitMQ if you are using
    ``om_enable_rabbitmq_high_availability``.