The workload runner should abort execution is a query fails in a multi-user run.

Currently, we coalesce the results and do not properly catch a failure if one of the
threads has a failed query and exit_on_error is set to True. This patch ensures that we
exit before the next query is run.

Change-Id: Ie650e0f547874386c79c78982ea9916f33e18cda
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2696
Reviewed-by: Ishaan Joshi <ishaan@cloudera.com>
Tested-by: jenkins