jenkins@juju-qa-maas-server-1:~$ maas env20 devices create parent=node-d8c99e5a-71e8-11e5-a1d4-525400c43ce5 hostname=juju-anything mac_addresses=aa:bb:cc:dd:ee:f0 -d
400 BAD REQUEST

         Connection: close
       Content-Type: application/json
               Date: Fri, 09 Sep 2016 16:33:30 GMT
             Server: TwistedWeb/16.0.0
             Status: 400
  Transfer-Encoding: chunked
               Vary: Cookie
    X-Frame-Options: SAMEORIGIN

{"system_id": ["Node with this System id already exists."]}