HBASE-9789 Change logging for Coprocessor exec call to trace

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.94@1533178 13f79535-47bb-0310-9956-ffa450edef68
HBASE-9749: Custom threadpool for Coprocessor obtained HTables

git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/0.94@1533185 13f79535-47bb-0310-9956-ffa450edef68