TEZ-1647. Issue with caching of events in VertexManager::onRootVertexInitialized. (Jeff Zhang via hitesh)

(cherry picked from commit e0fe9aaeacb43e8aa3fe1d0a5413b26598d076ed)
TEZ-1470. Recovery fails due to TaskAttemptFinishedEvent being recorded multiple times for the same task. (Jeff Zhang via hitesh)

(cherry picked from commit 4b5b20e23638965495f186fb6fc28f5d82346b80)