Tiny setting with a stochastic next-frame model.

def rlmb_tiny_stochastic():
  """Tiny setting with a stochastic next-frame model."""
  hparams = rlmb_ppo_tiny()
  hparams.epochs = 1  # Too slow with 2 for regular runs.
  hparams.generative_model = "next_frame_basic_stochastic"
  hparams.generative_model_params = "next_frame_basic_stochastic"
  return hparams