Meta server: add chunk server access token issue time to the allocate and lease acquire and renew response to allow client avoid chunk server access token parsing. Fix chunk allocate response: do not add chunk server and chunk access tokens if the client was not authenticated or chunk access token valid time isn't positive.
Kfs io lib: do not emit invalid delegation token if signature key length is 0 or less, or if tokens valid time interval is not positive.
Client lib: implement chunk server and chunk access token parsing with chunk allocate rpc.