[tune] Change pickle to ray.cloudpickle -- support large models (#12958)

* Change pickle to ray.cloudpickle

* Change pickle import to ray.cloudpickle

python/ray/tune/trainable.py

@@ -5,7 +5,7 @@ from datetime import datetime
 import copy
 import logging
 import os
-import pickle
+import ray.cloudpickle as pickle
 import platform
 
 from ray.tune.utils.trainable import TrainableUtil

python/ray/tune/utils/trainable.py

@@ -5,7 +5,7 @@ import shutil
 from typing import Dict, Any
 
 import pandas as pd
-import pickle
+import ray.cloudpickle as pickle
 import os
 
 import ray