spec: change the ownership of cache directory

spec: change the ownership of cache directory

In a50c473ad6c9 ("qemu: move temp file of screenshot and memorypeek to
per-domain dir") and c4f3c955d578 ("qemu: don't change ownership of
cache directory"), I move the temporary files of screenshot and
memorypeek from the cache directory to per-domain directory, and the
only user of the cache directory is the domain capabilities currently.
Since the domain capabilities are used by libvirtd, no need to set the
ownership of the cache directory to qemu_user and qemu_group.

Signed-off-by: Peng Liang <liangpeng10@huawei.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>