files, included 'upstream' qemu dropped, bconds

– 'xen-qemu' dropped. There is not point in maintaining two 'upstream'
  qemu builds in PLD, especially that this brings a lot of 'hidden'
  build dependencies here for things hardly useful.
- dropped BR needed only for that qemu build (ceph-devel, spice-*)
- xen-qemu-traditional made optional. This is only needed for those who
  need compatibility with old VMs based on this qemu fork. When disabled
  no build dependencies for the hardware emulation is needed
- xend bcond added. xend will be gone in the next major Xen release
- blktap1 bcond added
- xsm/flask bcond added
- %files updated for the 4.0.0 build, including the new bconds