Fix clear grad in acceptance test
Fix clear grad in acceptance test

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