Intégration Continue

As described in:
https://stackoverflow.com/questions/20335418/jenkins-stop-serving-static-files-after-a-couple-of-days
https://issues.jenkins-ci.org/browse/JENKINS-17526

While waiting for the fix, and as Jenkins does a lot in /tmp, we should probably set private_tmp=true and fix existing runtime.json files with -Djava.io.tmpdir=.

We chose to set private_tmp=false and increase /tmp. But we may want to turn back, and increase /opt.

BTW, why don't we have a specific LVM volume for /opt/jenkins-farm ?