Use vault repo for RHEL 8
Use vault repo for RHEL 8

Train has been archived to vault for RHEL 8 and this breaks CI currently.

Change-Id: Ia77026617f993169e46ef76ced3468b5e4fa8bfc
Signed-off-by: Lance Albertson <3161cdc7bf197e4c3a35b9cbe358c79910f27e90@osuosl.org>

openstack/cookbook-openstack-common,openstack/cookbook-openstack-common