Add AveragePool tests

[wjj19950828]

Create A Good Pull Request

下面的文字请保留在PR说明的最后面，并在提完PR后，根据实际情况勾选确认以下情况

Please check the follow step before merging this pull request

• [x] Python code style verification
• [x] Review all the code diff by yourself
• [ ] All models(TensorFLow/Caffe/ONNX/PyTorch) testing passed
• [x] Details about your pull request, releated issues

If this PR add new model support, please update model_zoo.md and add model to out test model zoos(@wjj19950828)

• [ ] New Model Supported
• [x] No New Model Supported

Do follow contributes

1、添加AveragePool单测 2、修复auto_pad属性问题 3、修复pad处理问题

• ONNX x1_begin、x2_begin、x1_end、x2_end
• Paddle x1_begin、x1_end、x2_begin、x2_end

4、修复Mod op，目前仅支持int类型，float类型paddle与np.fmod不对齐