Only Requires: libvirt-daemon-kvm on arch that have it
    
    Not all arch support libvirt-daemon-kvm, but we were unconditionnally
    requiring it. This commit conditionnally Requires libvirt-daemon-kvm,
    and also requires libvirt-daemon-qemu for arch that would not have
    kvm.
    This comes in complement of the ExclusiveArch added in the previous
    commit so won't be excercised for now.