report crashes that happen outside a test suite

Currently crashes that happen outside a test suite (such as those happening when global c++ objects are destroyed) are ignored and run-tests will fail with no error reports. This fixes the issue by detecting that the task has crashed using `terminationReason`, and generating a dummy testsuite and test that reports it.

I have included a dummy project/test which illustrates this issue.

Test Plan:

Running xctool on the included test generates a dummy test that shows
the crash.

```
  xctool run-tests -only CrashOnStaticInitExitTests -project \
    xctool/xctool-tests/TestData/TestsThatCrash/TestsThatCrash.xcodeproj \
    -scheme TestsThatCrash -sdk iphonesimulator6.1 -arch i386
```