setting the gotUncaughtSignal flag in the OCUnitIOSAppTestRunner

Summary: The OCUnitIOSAppTestRunner always set the gotUncaughtSignal argument to false, but this flag is used to determine if handleEarlyTermination should be called.

Test Plan:
- Run test cases on the iOS simulator that cause the process to crash
- Observe that the iOS simulator crashes, but the output counts any not run tests as "failures" included in the overall count
- Trigger failures in the installation process, observe that tests that haven't been run are still included.