add cancelAsyncCallback method to OperatorBase (#21492)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21492
If one async operator failed, async_scheduling net currently only marks all scheduled async operators as finished without cancelling the callbacks.
The new behavior is to cancel the callbacks first, then set event status to finished.
Reviewed By: ilia-cher
Differential Revision: D15702475
fbshipit-source-id: 55a1774d768b2e238bab859b83332f1877a001ca
