Make `centralized_db` driver as default cache driver

Making newly introduced `centralized_db` driver as default cache
driver for glance so that it can be tested in available CI jobs.

New cache driver `centralized_db` needs `worker_self_reference_url`
in glance-api.conf file otherwise glance api service will fail to
start.

Related blueprint centralized-cache-db
Depends-On: https://review.opendev.org/c/openstack/glance/+/899871

Change-Id: I75267988b1c80ac9daa5843ce8462bbac49ffe27
1 file changed