ENG-6699 Fix voltcli return code.

So I'm not sure this is going to be safe, but I don't know what possible values return_code has coming in to here.
See http://www.tldp.org/LDP/abs/html/exitcodes.html or any number of searches like it. It seems like certain return codes are not awesome ideas.

Why not just return 1 if return_code != 0?