buffet: Allow passing verbosity level to buffet. Example: restart buffet V=2 BUG=None TEST=Restarted the service manually. Change-Id: I003a9518bee14a98a06de7c6f96b82cd99c85383 Reviewed-on: https://chromium-review.googlesource.com/220540 Tested-by: Anton Muhin <antonm@chromium.org> Commit-Queue: Anton Muhin <antonm@chromium.org> Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>