Support gtest skipped tests

With recent versions of gtest it is possible to skip tests at run time. This is useful if for instance a test precondition fails. (Hence the test results are meaningless, if your preconditions are not satisfied).

You can skip a test at run-time by calling GTEST_SKIP(). But right now, QtCreator does not show the test as skipped (like it does for disabled tests). It would be nice to see that a test was skipped.