[SPARK-2871] [PySpark] Add missing API

Try to bring all Java/Scala API to PySpark.
It will help for debug, you can collect parts of the RDD to investigate with them.

It also be helpful if we have an API called slice(start, [end]) to select parts of the partitions. DPark has this kind of API, it help us a lot, Narrow down the data to do fast debugging.