conpaas-core: do not fail if create_nodes is called with count=0


git-svn-id: svn://svn.forge.objectweb.org/svnroot/contrail/trunk/conpaas@5268 ef35cc4a-2640-4bbf-98bc-65920db7d8ae
conpaas-director: default to 0 slaves in cpsdirector.manifest


git-svn-id: svn://svn.forge.objectweb.org/svnroot/contrail/trunk/conpaas@5269 ef35cc4a-2640-4bbf-98bc-65920db7d8ae