qemu: parse: Validate that the VM has at least one cpu
qemu: parse: Validate that the VM has at least one cpu

Libvirt's code relies on this fact so don't allow parsing a command line
which would have none.

Libvirtd would crash in the post parse callback on such config.

andreabolognani/libvirt,taget/libvirt,eskultety/libvirt,jfehlig/libvirt,libvirt/libvirt,nertpinx/libvirt,VenkatDatta/libvirt,datto/libvirt,libvirt/libvirt,taget/libvirt,zippy2/libvirt,libvirt/libvirt,libvirt/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,olafhering/libvirt,crobinso/libvirt,taget/libvirt,andreabolognani/libvirt,taget/libvirt,olafhering/libvirt,VenkatDatta/libvirt,crobinso/libvirt,jardasgit/libvirt,olafhering/libvirt,taget/libvirt,datto/libvirt,zippy2/libvirt,eskultety/libvirt,datto/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,olafhering/libvirt,zippy2/libvirt,eskultety/libvirt,andreabolognani/libvirt,datto/libvirt,VenkatDatta/libvirt,zippy2/libvirt,jardasgit/libvirt,nertpinx/libvirt,jardasgit/libvirt,andreabolognani/libvirt,nertpinx/libvirt,andreabolognani/libvirt,jfehlig/libvirt,crobinso/libvirt,jardasgit/libvirt,VenkatDatta/libvirt,fabianfreyer/libvirt,eskultety/libvirt,datto/libvirt,jfehlig/libvirt,jfehlig/libvirt,VenkatDatta/libvirt,eskultety/libvirt,crobinso/libvirt,fabianfreyer/libvirt,jardasgit/libvirt