After all of the discussions we had on
"https://review.opendev.org/#/c/670626/2", I studied all projects that
have an "oslo_messaging" section. Afterwards, I applied the same method
that is already used in "oslo_messaging" section in Nova, Cinder, and
others. This guarantees that we have a consistent method to
enable/disable notifications across projects based on components (e.g.
Ceilometer) being enabled or disabled. Here follows the list of
components, and the respective changes I did.

* Aodh:
The section is declared, but it is not used. Therefore, it will
be removed in an upcomming PR.

* Congress:
The section is declared, but it is not used. Therefore, it will
be removed in an upcomming PR.

* Cinder:
It was already properly configured.

* Octavia:
The section is declared, but it is not used. Therefore, it will
be removed in an upcomming PR.

* Heat:
It was already using a similar scheme; I just modified it a little bit
to be the same as we have in all other components

* Ceilometer:
Ceilometer publishes some messages in the rabbitMQ. However, the
default driver is "messagingv2", and not ''(empty) as defined in Oslo;
these configurations are defined in ceilometer/publisher/messaging.py.
Therefore, we do not need to do anything for the
"oslo_messaging_notifications" section in Ceilometer

* Tacker:
It was already using a similar scheme; I just modified it a little bit
to be the same as we have in all other components

* Neutron:
It was already properly configured.

* Nova
It was already properly configured. However, we found another issue
with its configuration. Kolla-ansible does not configure nova
notifications as it should. If 'searchlight' is not installed (enabled)
the 'notification_format' should be 'unversioned'. The default is
'both'; so nova will send a notification to the queue
versioned_notifications; but that queue has no consumer when
'searchlight' is disabled. In our case, the queue got 511k messages.
The huge amount of "stuck" messages made the Rabbitmq cluster
unstable.

https://bugzilla.redhat.com/show_bug.cgi?id=1478274
https://bugs.launchpad.net/ceilometer/+bug/1665449

* Nova_hyperv:
I added the same configurations as in Nova project.

* Vitrage
It was already using a similar scheme; I just modified it a little bit
to be the same as we have in all other components

* Searchlight
I created a mechanism similar to what we have in AODH, Cinder, Nova,
and others.

* Ironic
I created a mechanism similar to what we have in AODH, Cinder, Nova,
and others.

* Glance
It was already properly configured.

* Trove
It was already using a similar scheme; I just modified it a little bit
to be the same as we have in all other components

* Blazar
It was already using a similar scheme; I just modified it a little bit
to be the same as we have in all other components

* Sahara
It was already using a similar scheme; I just modified it a little bit
to be the same as we have in all other components

* Watcher
I created a mechanism similar to what we have in AODH, Cinder, Nova,
and others.

* Barbican
I created a mechanism similar to what we have in Cinder, Nova,
and others. I also added a configuration to 'keystone_notifications'
section. Barbican needs its own queue to capture events from Keystone.
Otherwise, it has an impact on Ceilometer and other systems that are
connected to the "notifications" default queue.

* Keystone
Keystone is the system that triggered this work with the discussions
that followed on https://review.opendev.org/#/c/670626/2

. After a long
discussion, we agreed to apply the same approach that we have in Nova,
Cinder and other systems in Keystone. That is what we did. Moreover, we
introduce a new topic "barbican_notifications" when barbican is
enabled. We also removed the "variable" enable_cadf_notifications, as
it is obsolete, and the default in Keystone is CADF.

* Mistral:
It was hardcoded "noop" as the driver. However, that does not seem a
good practice. Instead, I applied the same standard of using the driver
and pushing to "notifications" queue if Ceilometer is enabled.

* Cyborg:
I created a mechanism similar to what we have in AODH, Cinder, Nova,
and others.

* Murano
It was already using a similar scheme; I just modified it a little bit
to be the same as we have in all other components

* Senlin
It was already using a similar scheme; I just modified it a little bit
to be the same as we have in all other components

* Manila
It was already using a similar scheme; I just modified it a little bit
to be the same as we have in all other components

* Zun
The section is declared, but it is not used. Therefore, it will
be removed in an upcomming PR.

* Designate
It was already using a similar scheme; I just modified it a little bit
to be the same as we have in all other components

* Magnum
It was already using a similar scheme; I just modified it a little bit
to be the same as we have in all other components

Closes-Bug: #1838985

Change-Id: I88bdb004814f37c81c9a9c4e5e491fac69f6f202
Signed-off-by: Rafael Weingärtner <rafael@apache.org>