TEZ-1637. Improved shuffle error handling across NM restarts.
Contributed by Rajesh Balamohan.
(cherry picked from commit 62536218271317d8b8e57c7ce172d247a95db3ba)
TEZ-1479. Disambiguate (refactor) between
ShuffleInputEventHandlers and Fetchers. (sseth)
(cherry picked from commit 7be5830a908602ff91a07d3020f2dddf7705d48f)
TEZ-1665. DAGScheduler should provide a priority range instead of an exact priority (bikas)jps
TEZ-1479 addendum. Revert accidental change from previous commit.
(sseth)
(cherry picked from commit 71231c892deb40d4c7a0c9f948ea8d40ceb0ec6e)