Remove Tools/scripts/run_tests.py and make hostrunnertest. Just run
./python -m test --slow-ci, make buildbottest or make test instead.
Python test runner (regrtest) now handles cross-compilation and HOSTRUNNER. It
also adds options to Python such fast -u -E -W default -bb when
--fast-ci or --slow-ci option is used. Patch by Victor Stinner.