Fix Usage of rdo-release rpm
Fix Usage of rdo-release rpm

rdo-release.el8.rpm rpm points to latest RDO release,
so use it for master, for stable releases use corresponding
release rpm.

Change-Id: I508eceb00d7501ffcfac73d7bc2272badb241494

openstack-dev/devstack,nawawi/openstack,openstack-dev/devstack,nawawi/openstack