[SPARK-14731][shuffle]Revert SPARK-12130 to make 2.0 shuffle service compatible with 1.x

## What changes were proposed in this pull request?
SPARK-12130 make 2.0 shuffle service incompatible with 1.x. So from discussion: [http://apache-spark-developers-list.1001551.n3.nabble.com/YARN-Shuffle-service-and-its-compatibility-td17222.html](url) we should maintain compatibility between Spark 1.x and Spark 2.x's shuffle service.
I put string comparison into executor's register at first avoid string comparison in getBlockData every time.

## How was this patch tested?
N/A

Author: Lianhui Wang <lianhuiwang09@gmail.com>

Closes #12568 from lianhuiwang/SPARK-14731.