Suggestion: new provisioner

[dublx]

Hi, It would be good to have a provisioner (as in LOG/RUN) that forces running a command, regardless of whether it's been run previously. Something like NOCACHE. The use case is that there are situations where one has to run a command every-time (imagine getting a auth token for subsequent commands). Ideally one could also call stack with --nocache to force a complete run.

Cheers, Luis