Switch libvirt default service / sockets
    
    The monolithic libvirtd is being replaced by modular hypervisor
    specific daemons. For seemless migration we need to ensure the
    hypervisor daemon service units are enabled by default instead
    of libvirtd, to ensure auto-start on boot works for VMs. For
    other daemons only the socket units need enabling by default.
    
    https://fedoraproject.org/wiki/Changes/LibvirtModularDaemons
    
    Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>