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
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/5262
Reviewed-by: Martin Grund <mgrund@cloudera.com>
Tested-by: jenkins