Add lock_guard to cudnn batch_norm to be thread-safe
Add lock_guard to cudnn batch_norm to be thread-safe

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