Fix optimizer for not supporting all kinds of iterables

[OscarXZQ]

BUG

Traceback (most recent call last):
  File "train.py", line 95, in <module>
    main(args)
  File "train.py", line 48, in main
    model = CycleGANModel(opt)
  File "/home/xuzhiqiu/models/cycleGAN/cycleGAN.py", line 31, in __init__
    self.optimizer_G_A = flow.optim.Adam(itertools.chain(self.netG_A.parameters(), self.netG_B.parameters()), lr=opt.lr, betas=(0.5, 0.999))
  File "/home/xuzhiqiu/backup/oneflow/build/python_scripts/oneflow/python/nn/optimizer/adam.py", line 103, in __init__
    self.param_groups.append(ParamGroup(param, self._default_options))
  File "/home/xuzhiqiu/backup/oneflow/build/python_scripts/oneflow/python/nn/optimizer/optimizer.py", line 36, in __init__
    assert "params" in parameters
AssertionError

原因是，在 optimizer.py 里面

if isinstance(parameters, GeneratorType):
            self._parameters = list(parameters)
            self._options = default_options
else:  # Dict
            assert "params" in parameters
            self._parameters = list(parameters["params"])
            self._options = default_options
            for key in self._options:
                if key in parameters:
                    self._options[key] = parameters[key]

但pytorch对应的源码是这样的

param_groups = list(params)
if len(param_groups) == 0:
      raise ValueError("optimizer got an empty parameter list")
if not isinstance(param_groups[0], dict):
      param_groups = [{'params': param_groups}]

itertools.chain生成的确实是一个 iterable，但并不是generator type，所以会被我们这里写的if条件卡住。但Pytorch这里的写法不会卡住其他的 iterable 所以Pytorch可以运行那段代码但我们不行。

最后没有使用Pytorch的写法（过于奇怪），把原本check的generator type改成了collections.abc.Iterator，改了所有带这个判断的optimizer