Pull jenkins-job-builder related packages from backports or testing

Originally created by @bertagaz on #10242 (Redmine)

We currently pulled a newer version of JJB and its dependencies from Sid as soon as it entered in the Debian archive.

We may not want this to remain this way and pull them from jessie-backports or Stretch if not possible.

Edited May 15, 2020 by bertagaz