[MINOR] Process local update operation through operation queue

[wynot12]

This PR fixes the data consistency problem in the PS-collocation mode of Dolphin-on-ET.
Especially LDA app fails with EOFException, since its model array's length varies in runtime.

ET allows bypassing of operation queue when the operation is for local blocks.
It's quite efficient, since it minimizes overheads in data access.

However, allowing bypass to update operation has a problem, since this operation should be atomic. Without operation queueing, the operation is not guaranteed to be atomic.

This PR simply eliminates the problem by changing ET's update operation to use the remote access's routine also for local access.
However, it has unnecessary overheads in (de)serialization of key and update values, (and passing through loopback network interface; I have no idea about how much overhead it has.).
Let's optimize this part later, since it's not much critical.

[yunseong]

Thanks for the PR! I'm so glad that this change fixes the correctness issue we've suffered.
I'll merge this.