PIG-3965: Fix MR unit tests on tez branch

git-svn-id: https://svn.apache.org/repos/asf/pig/branches/tez@1598370 13f79535-47bb-0310-9956-ffa450edef68
Merge latest trunk changes

git-svn-id: https://svn.apache.org/repos/asf/pig/branches/tez@1598376 13f79535-47bb-0310-9956-ffa450edef68