Comment 8 for bug 1683440

This also breaks maas on the CLI:
bladernr@critical-maas:~$ maas admin machine deploy -d pbrbtr distro_series=xenial
500 INTERNAL SERVER ERROR

         Connection: close
       Content-Type: text/plain; charset=utf-8
               Date: Mon, 17 Apr 2017 20:11:21 GMT
             Server: TwistedWeb/16.0.0
             Status: 500
  Transfer-Encoding: chunked
               Vary: Cookie
    X-Frame-Options: SAMEORIGIN

not enough values to unpack (expected 2, got 1)