IMPALA-1439: Make sure all errors are fetched

This patch will make sure that all error and warning messages are
fetched from impala. Before this patch, error messages that would occur
after the first row was retrieved would not be catched correctly.

Change-Id: I82a9a1c810e2ffabc7e56c996276082548ced805
(cherry picked from commit c357f530963673859be33726e8e5a896d77de097)
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/5263
Reviewed-by: Martin Grund <mgrund@cloudera.com>
Tested-by: jenkins