qemu_driver: fix existance vs existence typo
qemu_driver: fix existance vs existence typo

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