qemu: Destroy whole memory tree
    
    When removing path where huge pages are call virFileDeleteTree
    instead of plain rmdir(). The reason is that in the near future
    there's going to be more in the path than just files - some
    subdirs. Therefore plain rmdir() is not going to be enough.
    
    Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
    Reviewed-by: John Ferlan <jferlan@redhat.com>