For a long timer we've had the ability to build each libvirt
driver as a loadable module. We have never used this by default
and as a result it constantly bit-rots.
This series fixes various bugs, and then enables it by default
in configure. It also makes the PRMs use the loadable modules,
adding new new sub-RPMs for each module. We can now finally
install minimal libvirt binaries for each hypervisor.
ie yum install libvirt-kvm
will not pull in Xen libraries!