gluon random crop and resize on gpu

gluon_random_crop_resize.py

# 256x256
data = batch.data[0].as_in_context(ctx)

# random crop resize to 224x224
data_elems = nd.split(data, num_outputs=batch_size, axis=0)
for b in range(batch_size):
    xy0 = random.randint(0, 32)
    xy1 = random.randint(256-32, 256)
    cropped = nd.slice(data_elems[b], begin=(None,None,xy0,xy0), end=(None,None,xy1,xy1))
    cropped_resized = nd.contrib.BilinearResize2D(cropped, height=224, width=224)
    data_elems[b] = cropped_resized
data = nd.concat(*data_elems, dim=0)