Optimize local access routine of update and get operation

[wynot12]

#10 has fixed concurrency bug in local access of update operation.
However it exploits remote access routine for local access, which has unnecessary overheads (e.g., serialization of key, update value. passing loopback interface).

We can further optimize the local access routine of update operation.

[wynot12]

#14 introduces the same inefficiency in get APIs.