HIVE-3255: Add DBTokenStore to store Delegation Tokens in DB (Ashutosh Chauhan and Deepesh Khandelwal via Gunther Hagleitner)

git-svn-id: https://svn.apache.org/repos/asf/hive/trunk@1507752 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd