openstack: add 8.8.8.8 as a last resort resolver
openstack: add 8.8.8.8 as a last resort resolver

Signed-off-by: Loic Dachary <5971e5274f1f0ba5329cf4a93393d8fbe5224c44@redhat.com>

SUSE/teuthology,SUSE/teuthology,dmick/teuthology,ceph/teuthology,dreamhost/teuthology,ceph/teuthology,ktdreyer/teuthology,robbat2/teuthology,robbat2/teuthology,caibo2014/teuthology,ktdreyer/teuthology,dmick/teuthology,caibo2014/teuthology,SUSE/teuthology,dreamhost/teuthology,dmick/teuthology