Chunk server: fix write sync op chunk server and chunk access forwarding by copying access from received write sync op. Make write sync op chunk checksum verification trace messages more uniform by always emitting chunk id and write position (offset). Write sync is now redundant / deprecated and perhaps it is about time to remove support for it, the only reason to support it a while longer is that making it work is slightly simpler that removing it.
Kfs client library: fix write sync support with authentication on by copying / setting up chunk access with write sync op if / when write reply isn't supported. Write reply isn't supported only with old deprecated write protocol. With authentication on write reply should be always supported, unless it is turned off by configuration for testing purposes.
Kfs client lib: do not attempt to load configuration with QFS_CLIENT_CONFIG environment variable if the variable value is an empty string.