Add a failfast command-line option to runner.py

[aardappel]

This is functionality already exposed by TextTestRunner.

[sbc100]

Thanks for doing this. Does this work with the parallel test runner?

[sbc100]

It seems not. For example, if i force all dylink tests to fail then run wasm2 test suite with --failfast it still tries to runs everything it seems:

./tests/runner wasm2 --failfast --skip-slow
...

----------------------------------------------------------------------
Ran 754 tests in 53.236s

FAILED (failures=72, skipped=26)

[sbc100]

72 failures.. but ran all 754 tests

[aardappel]

Yes, it be nice if it worked with parallel tests too.. I guess I usually have all the test debugging stuff on anyway which turns that off.

[sbc100]

Would be cool to combine with some kind of "restart-suite-from-last-failure" feature too.. so one could iterate through the test suite fixing one thing at a time.

[aardappel]

that would have saved me a lot of time, yes