report crashes that happen outside a test suite

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
```
Merge pull request #73 from facebook/yiding/fix-test-crash-reporting

report crashes that happen outside a test suite