Update promote-image script to work with RHEL8
Update promote-image script to work with RHEL8

Change-Id: I108ed02a44b07c4a8357c2aa96e2bf19fc282c98

redhat-openstack/rdo-infra,rdo-infra/ci-config,rdo-infra/ci-config,rdo-infra/ci-config,rdo-infra/ci-config,redhat-openstack/rdo-infra,redhat-openstack/rdo-infra,redhat-openstack/rdo-infra