Tests from other tekton project on releases

[vdemeester]

Related to latest release (0.5.2) that include few problems, with the one of interest here being #1075, a controller panic.
We decided during the post-mortem brainstorm, that we need to run other project's tests (as much as possible) while doing the release (or on what commit we are releasing).

In a gist this means:

• Running tektoncd/cli e2e tests
• Running tektoncd/dashboard e2e tests
• Running tektoncd/triggers e2e tests
• More later one ? (maybe something on catalog if we have some e2e tests other than validation)

All of this should be using Task and Pipeline as much as possible.

This issue is here to track that work.

/cc @bobcatfish

[bobcatfish]

@afrittoli i've heard a rumor that you are taking this on?

[bobcatfish]

Our dogfooding in the "robocat" cluster should get us most of the way to this https://github.com/tektoncd/plumbing/tree/master/robocat!