[rancid] Issue with nx-os after switch upgrades

[heasley]

Thu, Mar 05, 2015 at 01:43:25AM +0200, Alan McKinnon:
> I never could understand why Invalid Command would be a fatal error -
> if the device can't do it, the script should just move past it and deal
> with the output it *can* handle.

because sometimes the command *should* exist.  its has caught o/s bugs in
the past.  if it may exist, then we return 1 when it is missing.