fix test_variable not to use node
fix test_variable not to use node

wkentaro/chainer,okuta/chainer,niboshi/chainer,jnishi/chainer,jnishi/chainer,hvy/chainer,wkentaro/chainer,ktnyt/chainer,keisuke-umezawa/chainer,hvy/chainer,jnishi/chainer,ktnyt/chainer,wkentaro/chainer,jnishi/chainer,niboshi/chainer,okuta/chainer,hvy/chainer,keisuke-umezawa/chainer,tkerola/chainer,niboshi/chainer,okuta/chainer,chainer/chainer,pfnet/chainer,keisuke-umezawa/chainer,keisuke-umezawa/chainer,chainer/chainer,hvy/chainer,niboshi/chainer,ktnyt/chainer,chainer/chainer,chainer/chainer,ktnyt/chainer,okuta/chainer,wkentaro/chainer