Add "fail-fast" option to yaml-tests

[ElijahLynn]

Add "fail-fast" option to yaml-tests so the first failure will fail the entire run and not keep going.

[ElijahLynn]

Discussed with team and we agreed that a test level flag would make more sense. e.g.

fail-fast: true that we can add to each test, with it defaulting to false.

[ElijahLynn]

Could probably still have a global --fail-fast option and maybe even allow it to be set globally inside the tests.yml file, as a global key.