HIVE-8496: Re-enable statistics [Spark Branch] (Chao via Xuefu)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/spark@1633210 13f79535-47bb-0310-9956-ffa450edef68
HIVE-8436: Modify SparkWork to split works with multiple child works [Spark Branch] (Chao via Xuefu)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/spark@1633268 13f79535-47bb-0310-9956-ffa450edef68
merge upstream/spark