Comment 2 for bug 1529143

We hard depend on unittest2 these days, so we should just use unittest2.SkipTest.

If we don't use the unittest2 one, we end up with the wrong exception class, and things go badly.

I think we can delete TestSkipped now, but we should not change the preference - go through our git history and you'll see it was inverted (and buggy) in the past.