Create value `cancelled` for `run`'s `when`


It’s useful to have cleanup stanza. This can be done with when: always. However, this is not done whenever the build is cancelled. It would be useful to also allow a when: cancelled.

Cancelled build post hook commands

+1 . We are cleaning up things after running tests and the only moment that our env ends up dirty is when a build gets cancelled since the tear-down step that we set up with when: always is not running then…

Is there any other why to do so that we are missing?