https://build.spring.io/browse/INT-MASTER-1042
The `verifyShutdownWithWait()` test uses extra thread for waiting for
the `TaskScheduler` to finish its tasks.
Also the test doesn't verify the actual behavior at all
* Move `awaitTermination()` to the assert
* Decrease `delay` for the message
* Assert the latch from the handler to be sure that message is scheduled
properly even if `destroy()` call, thanks to required
`waitForTasksToCompleteOnShutdown = true`
7113236e24