Add `project-description-setter` plugin support to jenkins-job-builder

[patcon]

Currently using jenkins-job-builder to make managing job templates simpler. It supports everything we need except this plugin:
https://wiki.jenkins-ci.org/display/JENKINS/Project+Description+Setter+Plugin

However, it should be extensible, if we want to contribute back:
http://ci.openstack.org/jenkins-job-builder/extending.html

(low priority)