Summary:
EventBaseAtomicNotificationQueue is now what used to be just AtomicNotificationQueue.
In the future, this allows reusing AtomicNotificationQueue with other types of executors.

(Note: this ignores all push blocking failures!)

Reviewed By: andriigrynenko

Differential Revision: D24878180

fbshipit-source-id: d719e31c7194cb2dd6d57a103814581b802a9250