By default when deploying the openstack AIO, it will deploy
openstack ocata release on ubuntu xenial, which by now is quite
old and largely unsupported. This change updates these default
overrides to train and bionic respectively in order to bring
the default settings to more recent/supported releases.
Change-Id: I9b6e1120101767356413b1341828dc8d39bc9b3c
01a1ab2ecc