HIVE-5080: Add hook to do additional optimization on the operator plan in tez (Gunther Hagleitner)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/tez@1514096 13f79535-47bb-0310-9956-ffa450edef68
HIVE-5097: Update DagUtils to reflect changes in Tez API (Gunther Hagleitner)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/tez@1514100 13f79535-47bb-0310-9956-ffa450edef68