[nozzle] decouple running pre-up.d/up.d/down.d/post-down.d from interface status (part 1)

provide the facility to do it via nozzle_run_updown but delegate the task to
the application.

This has the benefit of much better fine grained control over errors during those
code paths.

Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>