submitted tasks are not drained in tests expecting a failure

[McFoggy]

in bulkhead tests using Utils#loop() and expecting an Exception to be thrown, the submitted Future tasks are not drained at the end of the loop. They are drained only in case of success.

When using in your implementation a single threadpool for asynchronous bulkhead operations this make later tests to start with a threadpool that is possibly already filled making the later test to fail.