HBASE-8283 Backport HBASE-7842 Add compaction policy that explores more storefile groups to 0.94

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.94@1491546 13f79535-47bb-0310-9956-ffa450edef68
HBASE-8683 Add major compaction support in CompactionTool (Jerry He)

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.94@1491599 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/0.94' into 0.94-gd
Merge remote branch 'origin/0.94-gd' into fb-YAHOO-317-0.94-gd