The devstack cache steps were being run as the ubuntu user; make
sure they are run as jenkins.
Also update the nodepool configuration file to current values and
include the jenkins credential id.
Change-Id: Icbe8bee3b1800e28034cd36d4d328a6793d55b0e
We have a cgit server now, which means we should replace
all references to github with references to git.openstack.org.
Change-Id: I68ad1ce514fb4326c7d9940b5a84999af5b58562
