AMQP-347: SMLC: catch ShutdownSignalException

JIRA: https://jira.springsource.org/browse/AMQP-347

* Catch `ShutdownSignalException` in the `AsyncMessageProcessingConsumer` task
* Log it under DEBUG and mark Container (aborted = true) to `stop()`
* Add test to verify `SMLC.logger` after `connectionFactory.destroy()`