Config generator fails with lazy messages

Entry points from modules loaded from projects may have help text
that is i18n lazy enabled, which causes a failure because
gettextutils.Message (a subclass of six.text_type) explicitly
does not support concatenation.  Change from using concatenation
to using format (%) to allow six.text_type to do the right thing.

Change-Id: Ie60c569ae6fe227e16eef4a3281cf042732addc3
Closes-Bug: #1280826
Merge "Config generator fails with lazy messages"