Unskip Integ test `test_hp_contract_mpi_script` for SageMaker Train

Integ test `test_hp_contract_mpi_script` in [test_model_trainer.py](https://github.com/aws/sagemaker-python-sdk/blob/master/sagemaker-train/tests/integ/train/test_model_trainer.py) was skipped for some reson, we need to unskip it since it is critical test. While there are some bugs/config issues in the test, we need to fix it until it get passed.

从 sagemaker-train/tests/integ/train/test_model_trainer.py 开始，找到被跳过的测试 test_hp_contract_mpi_script。运行集成测试以确定其配置或运行时失败，然后解决报告的问题并移除跳过设置。当该测试能够在 SageMaker Train 中成功通过时，即表示完成。

由索引模型根据 Issue 内容生成。