Use default "ds512M" advance image in older stable branches (II)

This patch amends [1], setting the default advance image "ds512M" for
Designate scenario jobs in older stable branches.

Related-Bug: #1940243

[1]https://review.opendev.org/c/openstack/neutron-tempest-plugin/+/806119

Change-Id: Ied79caa66727f4df09fcbe8e4ec302c326862256
4 files changed