Changing the topic currently changes the service_name. This
breaks the service, as the service_name is also used to
load the appropriate configuration seection for the service.
> self._service_config = CONF['service:%s' % self.service_name]
* Renames cfg option [service:<name>].<name>_topic to [service:<name>].topic
* Removed previously unused configs related to topics.
* Added topic override for producer.
* Added test coverage.
Closes-Bug: #1832799
Change-Id: I16385361ec25025aa533df80793dfc4d22151cbb
fcb3290be7