HBASE-8778 Region assigments scan table directory making them slow for huge tables

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.95@1510978 13f79535-47bb-0310-9956-ffa450edef68
HBASE-9126 Make HFile MIN VERSION as 2

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.95@1511024 13f79535-47bb-0310-9956-ffa450edef68