Use ProductVersion when constructing CFFIXED_USER_HOME

[#227]
renaming some util functions to be more self explanatory

GetProductVersion -> GetProductVersionForSDKVersion
GetSDKVersionString -> GetIPhoneSimulatorVersionsStringForSDKVersion
GetSDKProperty -> GetSystemVersionPropertyForSDKVersion
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.
Merge branch 'leifaffles/xctool-ios-runner-fix' of https://github.com/facebook/xctool into leifaffles/xctool-ios-runner-fix

Conflicts:
	xctool/xctool/OCUnitIOSAppTestRunner.m