FR: make return value non-zero when no servers found

[aporcupine]

When running rack servers instance list with flags such as name or image and no results are returned it would be useful if the return value was non-zero.

This would make it much easier to use if statements when scripting things.

[jrperritt]

Can you show me what you're using now and what you'd change it to if the return value was non-zero?