Prior to this change, the ceilometer-agent charm receives RMQ
configuration details via the ceilometer charm. This makes it
a bit of a snowflake.
Refactor RMQ integration to require a direct relation to the
rabbitmq-server charm; information provided on this relation
will superceed any information currently provided via the
charms relation with ceilometer, ensuring that there is no
disruption to service during a charm upgrade before the new
relation is added.
Switch to using [DEFAULT]transport_url for RMQ configuration,
making use of the new ch template for SSL and HA configuration
in [oslo_messaging_rabbit].
Change-Id: Ie637ec5162461826505cea39bde6829e036fa1f2
Closes-Bug: 1817672
54530ab595