Pipeline: Run CI's YAML tests as a `go test` instead of bash scripts

[sbwsg]

Expected Behavior

YAML tests can be run as part of a go test suite, maybe with their own build tag. Failures in the tests should be correctly highlighted in the log output / prow error highlighting.

Actual Behavior

We currently run YAML tests through a series of bash scripts. Their failure isn't reported accurately by the log output / prow error highlighting - the integration suite will show "0 / 29 failures" but grepping through the log output will indicate that the YAML tests failed or did not complete.

Steps to Reproduce the Problem

1. Make a PR against Tekton Pipelines
2. Wait for the integration suite to fail
3. Grep through the integration logs for "YAML" and find errors

[thomaschandler]

I'd like to work on this! This will be my first contribution, so it will take me some time to ramp up!

[vdemeester]

/assign @thomaschandler

[bobcatfish]

yaaaaaassss!!!!

Thanks again for this @thomaschandler and for your patience with me duplicating your efforts and the review being prolonged. Really excited to have this in!!!