presence/absence of @Asynchronous should not modify the @Bulkhead behavior

[Ladicek]

The @Bulkhead annotation should itself configure whether semaphore isolation or "threadpool" isolation should be used. We can easily do that by changing the default value of waitingTaskQueue to 0 (where 0 means semaphore isolation), and whenever user configures it to > 0, "threadpool" isolation (which is in fact just an additional queue) is used.