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
Remote request should not do the lookup for where the block is. The server should do that logic.

Please remove this logic from the remote request. If you want to say how deep the request can go, that is fine; but not which one