Minor improvements to table sink/writer.

Change-Id: I7b354ccb5f1a366fa2fb565d895ac56f744cc9d3
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/5107
Reviewed-by: Henry Robinson <henry@cloudera.com>
Tested-by: jenkins
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/5257
Reviewed-by: Nong Li <nong@cloudera.com>