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

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1482697 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/trunk@1482705 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd