HIVE-7211 : Throws exception if the name of conf var starts with "hive." does not exists in HiveConf (Navis reviewed by Vaibhav Gumashta)

git-svn-id: https://svn.apache.org/repos/asf/hive/trunk@1605245 13f79535-47bb-0310-9956-ffa450edef68