Comment 4 for bug 1361071

OK a simple repro case from trunk is:

- set up and activate a venv
$ plainbox run -i 2013.com.canonical.certification::__disk__
===========================[ Running Selected Jobs ]============================
----------------------------------[ __disk__ ]----------------------------------
ID: 2013.com.canonical.certification::__disk__
(Command output hidden)
ERROR plainbox.ctrl: Ignoring invalid generated job 2013.com.canonical.certification::staging/disk/stats_{name}: Problem with field requires: wrong
Outcome: job passed
==================================[ Results ]===================================
2013.com.canonical.certification::__disk__: pass