Handle consumer cancellation notifications using work pool

Otherwise blocking operations like queue.declare or basic.consume
will never return when executed on the main loop.
Rename class
Don't use wildcard imports
Refer to correctly spelt test case
Formatting
Moving methods around to match DefaultConsumer
Formatting
Use a countdown latch to synchronize
await up to 500 ms
Formatting
No need to do passive queue.declare here any more
Bump wait period to 2 seconds

Slow CI server is slow
Remove a confusing comment

It was automatically inserted by IDEA.
Swap arguments in ConsumerDispatcher#handleCancel

to match all the other methods
Merged bug25708 into default