MQTTProducerTest fails once you enable this testcase. This is disabled here:
Although this may be a known issue as it's explicitly disabled, I'm filing this anyway since I couldn't find any corresponding JIRA.
It fails with different error on 2.12.2 and current upstream master, but both case show the producer can't send messages through the MQTT producer correctly. I think there is an issue in camel-mqtt since I hit same issue in our application (https://issues.jboss.org/browse/SWITCHYARD-2221), but even if the problem is in the testcase, it still needs to be replaced with appropriate testcase to verify MQTT producer works correctly.