[PipeSleepStrategy] prevent the still present race to cqes with the completer

The previous race which I tried but in fact can not be fixed alone with
waitInflight flag is now described in the code comment in
PipeSleepStrategy::sleep().

To completely prevent the completer and the worker racing to the
new work notifications cqes we repurpose the cq_lock to ensure the
completer is always observing and honoring the waitInflight flag.

Also add an onNewWorkNotification callback to keep most sleep related
code and logic in PipeSleepStrategy.