Function _BatchNormGrad

Returns the gradients for the 3 inputs of BatchNorm. Args: grad_y: A `Tensor` of 4 dimensions for gradient for y. x: A `Tensor` of 4 dimensions for x. scale: A `Tensor` of 1 dimension for scaling. pop_mean: A `Tensor` of 1 dimension for the population mean. Only used when is

(grad_y,
                   x,
                   scale,
                   pop_mean,
                   pop_var,
                   epsilon,
                   data_format,
                   is_training=True)