rpm: fix upgrades when RBD is disabled in a new version

rpm: fix upgrades when RBD is disabled in a new version

We previously had to disable RBD on 32-bit platforms since Ceph has
dropped all support for 32-bit. Unfortunately anyone with the RPM
libvirt-daemon-driver-storage-rbd installed on 32-bit now has a
broken upgrade path.

To fix this we must make libvirt-daemon-driver-storage-core
have an Obsoletes: libvirt-daemon-driver-storage-rbd < $VER-$REL

Reviewed-by: Erik Skultety <eskultet@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>