Coadmin

Coordinator Admin Server and Client Side related changes. 
storeName is not a map, it is an element from the List<String> requestedStoreNames.

Lists in Java can contain null elements. Currently, there should be no caller of this function that includes a null in the stores it requests, but this was more of a protection against the future.

Also, while I understand that null and empty CAN mean different things, I think in this case they do both mean that they can be safely ignored, so the sanity check can be compacted into a single if.