HBASE-8547 Fix java.lang.RuntimeException: Cached an already cached block

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.95@1482698 13f79535-47bb-0310-9956-ffa450edef68
HBASE-8547. Fix java.lang.RuntimeException: Cached an already cached block (Addendum to add better log)

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.95@1482706 13f79535-47bb-0310-9956-ffa450edef68