Fix stress runner exit issues

1. The stress runner in parallel run, regardless to the test failures
   returned with 0 (EXIT_SUCCESS) exit status.
2. Stress runner did not stopped run in serial execution, when the stop
   on first failure was enabled.

Change-Id: Ifb71c58a2f676f8a3427160dbc5cfeab61d13b56
Merge "Fix stress runner exit issues"