TEZ-1525. BroadcastLoadGen testcase (gopalv and sseth)

(cherry picked from commit 00c5a93f3b250facb957231eb2cee01854bb2369)

Conflicts:
	CHANGES.txt
TEZ-1667. Add a system test for InitializerEvents. (sseth)
(cherry picked from commit 99f2b8ee94cd9ed551fa380ed0411b4cc69f6d77)
TEZ-1668. InputInitializers should be able to register for Vertex state
updates in the constructor. (sseth)
(cherry picked from commit 63648fba216fc8e1caff629a023c73c2b8584aa3)
TEZ-1656. Grouping of splits should maintain the original ordering of splits within a group (bikas)
(cherry picked from commit fdebd19941c34f3d879a322e11cfe3642876b463)
TEZ-1396. Grouping should generate consistent groups when given the same set of splits (bikas)
(cherry picked from commit 7a802b13d19c09ffe7bf0c331e0fac7234d0063b)
TEZ-1210. TezClientUtils.localizeDagPlanAsText() needs to be fixed for session mode (Alexander Pivovarov via bikas)
(cherry picked from commit 1cee45da1be60fd1d0b71a84fe5875920931da5c)
TEZ-1629. Replace ThreadPool's default RejectedExecutionHandler in ContainerLauncherImpl to void abort when AM shutdown (zjffdu)

(cherry picked from commit 7cc5db92c588cf0712a2f4612708b8d32cfaf1a6)