DLlib: add enable_hdfs_load decorator

[lalalapotter]

Description

According to the customer feedback, there is no SparkContext error while loading HDFS file in ray workers, which is because users use enable_multi_fs_load decorator to load HDFS file and need SparkContext to get gateway of Scala service in each worker. This PR is to add enable_hdfs_load decorator, which is totally implemented in Python, to address the customer issues.

[hkvision]

Need to add a unit test