Chunk server: when creating a new chunk do not return status to the meta server before the corresponding disk file create completes. This is required to minimize the effect of the time gap between detection of a problem with a chunk directory and the actual chunk allocation rpc on the new chunk allocations. With this change the chunk allocation status returned to the meta server only when "open chunk / file status" completes. Open / create file failure detection before chunk allocation rpc completes allow the client to simply retry chunk allocation which can succeed with other chunk servers, or different device on the same chunk server.