HBASE-10074 consolidate and improve capacity/sizing documentation

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1547928 13f79535-47bb-0310-9956-ffa450edef68
HBASE-9489 Add cp hooks in online merge before and after setting PONR

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1547996 13f79535-47bb-0310-9956-ffa450edef68