fix timing and failure handling in testRestartingExpiry
...which was failing nearly all the time on my laptop
- publishing is async, so we don't know when the message has it the
  server and hence the expiry timer starts. We could introduce a
  confirm, but it's easier to just use the server restart as an
  indicator.
- when the assertion fails we still need to delete the
  queue. otherwise other tests using the same queue name, but
  different params, will fail.