Update opensuse version
Update opensuse version

Nova has newer qemu requirements which needs opensuse 15.2 to meet. The
infra opensuse 15 images are 15.2 now to accomodate that. Update
opensuse's supported version to match.

Change-Id: I6f3c5234920b185b2b0cd9c358371402f7a7b922

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