run-workload should exit with a non-zero error code if a query fails and abort_on_error is true

The exception raised by a child thread did not reach the main thread, so the
script exited with 0 instead of 1.

Change-Id: I09be9dc824386bf25a64af0323cbf78f6d006b91
Reviewed-on: http://gerrit.ent.cloudera.com:8080/3081
Reviewed-by: Taras Bobrovytsky <tbobrovytsky@cloudera.com>
Tested-by: jenkins