Remove dependency on cradle

[nc7s]

...as an effort of minimizing dependencies in Debian. Since the tests are meant to pass, I just unwrap()'d it.

JustRun is just an improvised name, as well as its placement. Do advice if you just don't like that.

[casey]

Good call!

I think it's fine to just call Command instead of adding a trait, since it's only three places, it's not really a huge amount of extra code. I pushed a diff to the PR which removes JustRun and uses Command directly.