Jenkins: Use private repository for all KIE (drools, jbpm, ...) builds to avoid false negatives

When certain jenkins jobs build in parallel, false negatives might arise because by default all slaves share the same hard drive, so they aall share the same local repository.

To fix this:
For all jenkins jobs on master and 6.0.x [1]:

• open the job configuration
• look for build steps
• in the maven build step, click on the button "Advanced"
• Enable the checkbox "Use private maven repository".

1 or 2 jobs might already have that checkbox enabled.

[1] so all jobs on these 2 urls:
https://jenkins.mw.lab.eng.bos.redhat.com/hudson/view/Drools%20jBPM/view/Master/
https://jenkins.mw.lab.eng.bos.redhat.com/hudson/view/Drools%20jBPM/view/Kie-6.0.x/