Add padding test for 3-dim array
Add padding test for 3-dim array

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