Revert "Fix for a race condition in LeaderLatch which resulted in spurious nodes being set in Zookeeper"

This didn't actually fix the race condition, just reduced its chances of happening.

This reverts commit ba4d078020887a88905a21b27d3adcf139d0a948.
Actual fix for the race condition, must be done by detecting a spurious node and explicitly deleting it
Added an event mechanism to LeaderLatch to allow clients to get notified of leadership changes