do not log stack trace for simulated exceptions in FailTask* unit tests
suppress stack trace dumps for simulated errors in unit tests.
suppress stack trace dump for runtime errors in failure unit tests
Merge pull request #731 from Microsoft-CISL/sergiym_no_test_exceptions

Suppress stack trace dumps for failure unit tests
Merge branch 'master' of https://github.com/Microsoft-CISL/REEF into reef_730