Coadmin

Coordinator Admin Server and Client Side related changes. 
This fatclients_config.avro only has "test" initially.
I don't see the point why we want to add "best":{} here. Similarly, we don't want to remove "identifier_string" from store "test" section.

In fact, the modification in this file is a result of coordinator admin command execution. Maybe we should put this file in .gitignore?