Comment 3 for bug 822666

There is the same type of error hiding in case a utils.execute calls fails:

in exception.py, see ProcessExecutionError

 message = _('%(description)s\nCommand: %(cmd)s\n'
                    'Exit code: %(exit_code)s\nStdout: %(stdout)r\n'
                    'Stderr: %(stderr)r') % locals()

description unfortunately may contain unicode from i18n.