HIVE-8718: Refactoring: move mapLocalWork field from MapWork to BaseWork (Reviewed by Szehon)
merged from trunk, r1636888 w/ corresponding Spark code changes

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/spark@1636910 13f79535-47bb-0310-9956-ffa450edef68