AMQP-417 Fix Failing Test

JIRA: https://jira.spring.io/browse/AMQP-417

Fixes: https://build.spring.io/browse/AMQP-MEIGHT-JOB1-212/test/case/144084713

- The executor thread returned its channel to the cache after the
   factory was destroyed.
- The `destroy()` method resets the connection; allowing forcing a new connection;
   it does not prevent the factory from being re-used.
- Although 'dead' channels can be returned to the cache, they will be detected on
   next use, and refreshed.
- Stop the executor before destroying the CCF to fix the test case.