node jobs: add createrepo rpms on slave

createrepo package is needed for example by:
http://jenkins.ovirt.org/job/ovirt-node-iso_master_merged/

Change-Id: I1bdd2b889b40f24ceed5d49b86c1318f543be9ef
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>