HIVE-4617: Asynchronous execution in HiveServer2 to run a query in non-blocking mode (Jaideep Dhok & Vaibhav Gumashta via Thejas Nair)

git-svn-id: https://svn.apache.org/repos/asf/hive/branches/branch-0.12@1521350 13f79535-47bb-0310-9956-ffa450edef68