Sort shuffle read improvements

Hi @sryza , I've done some improvements in current SortSHuffleRead, would you mind help reviewing this and give me some comments, thanks a lot!

1. copy memory shuffle block from off-heap to on-heap if memory is allocated with direct memory to control the off-heap memory size.
2. Some code style modification and better failure processing logic.
Yes, the first problem is actually a bug, while the second one seems like the same issue as [SPARK-4452](https://issues.apache.org/jira/browse/SPARK-4452).