[SPARK-13265][ML] Refactoring of basic ML import/export for other file system besides HDFS

jkbradley I tried to improve the function to export a model. When I tried to export a model to S3 under Spark 1.6, we couldn't do that. So, it should offer S3 besides HDFS. Can you review it when you have time? Thanks!

Author: Yu ISHIKAWA <yuu.ishikawa@gmail.com>

Closes #11151 from yu-iskw/SPARK-13265.