Rewrite `unittest.main()` with `sys.exit(pytest.main([__file__]))`

[verhovsky]

I'm using pytest with bazel. To get bazel to pick up the fact that a pytest test has failed you need to put this at the end of every *_test.py file:

if __name__ == "__main__":
    sys.exit(pytest.main([__file__]))

(See bazel-contrib/rules_python#240 )

It would be nice if this tool had an option to change the unittest-based snippet

if __name__ == "__main__":
    unittest.main()

with the pytest one.