TEZ-1731. OnDiskMerger can end up clobbering files across tasks with
LocalDiskFetch. (sseth)
(cherry picked from commit 57827160a8772858f667aacba65c6589234c641b)
TEZ-1735. Allow setting basic info per DAG for Tez UI. (hitesh)

(cherry picked from commit db4112cc0019b36c587503ad5673b4a7265cc91a)