Merge hierarchy store into Tachyon [TACHYON-33 sub-task 5 & 6]

Merge hierarchy store into Tachyon, which supports storing data on both memory and other storage(SSD HDD etc), client side and RPC interface are also modified accordingly

JIRA:
https://tachyon.atlassian.net/browse/TACHYON-38
https://tachyon.atlassian.net/browse/TACHYON-39
I think this logic (getting the storage ID of a block if its stored on the local machine) is repeated a number of times throughout TachyonFS. It would be nice to refactor it into its own function.