Add checksum for shuffle blocks

Shuffle data corruption is a long-standing issue in Spark. For example, in SPARK-18105, people continually reports corruption issue. However, data corruption is difficult to reproduce in most cases and even harder to tell the root cause. We don't know if it's a Spark issue or not. With the checksum support for the shuffle, Spark itself can at least distinguish the cause between disk and network, which is very important for users.