[SPARK-2288] Hide ShuffleBlockManager behind ShuffleManager

By Hiding the shuffleblockmanager behind Shufflemanager, we decouple the shuffle data's block mapping management work from Diskblockmananger. This give a more clear interface and more easy for other shuffle manager to implement their own block management logic. the jira ticket have more details.

Author: Raymond Liu <raymond.liu@intel.com>

Closes #1241 from colorant/shuffle and squashes the following commits:

0e01ae3 [Raymond Liu] Move ShuffleBlockmanager behind shuffleManager