Meta server: implement get layout variant that returns chunk info with an empty server list when no chunk replicas available.
Client library: implement get layout RPC flag that allows retrieving layout information even if some chunks have no replicas. Use this flag to retrieve layout information for file block enumeration, to make qfsfileenum work with the files with chunks with no replicas. Limit the number of entries retrieved by get layout to 256, and issue multiple get layout RPCs when needed to retrieve all file chunks. This is need to limit request's buffers on the meta server side, and ensure better fairness with other RPCs. Implement get data location for striped files: now get data location should return correct information populated with the data stripe locations. Return an empty data location entry when no chunk replicas are available for both striped and non striped files, instead of returning an error. Ensure that the i-node is not a directory, before retrieving data location, return EISDIR otherwise.
Qfs tool: implement -dloc command to allow retrieving file data location, with the primary intention to use it for testing and debugging.