and dm_targets_list ioctl to test if dm driver inside rump works.
It will be disable for now, because I need to find out why if I run this
test by atf-run it fails while running h_dm by hand works.
XXX. component.c in rump/libdm calls devsw_attach before dm_modcmd can do
that therefore unmodified modcmd returns error.
haad