HBASE-10993 Deprioritize long-running scanners

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1593137 13f79535-47bb-0310-9956-ffa450edef68
HBASE-7987 Snapshot Manifest file instead of multiple empty files

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1593139 13f79535-47bb-0310-9956-ffa450edef68