Chunk server: fix chunk meta data write error propagation with replication by passing the meta data (chunk header) write failure status to rename op completion handler. Only replication completion was affected by this bug, as in all other cases, except replication, the chunk io failure reported to the meta server and the chunk declared stale immediately after detecting io failure. With replication chunk version change results in two ops being queued one after another: chunk meta data version write with no completion, and file rename with the caller specified completion, i.e. replication completion. With this change the write failure status should be propagated to the rename op and, in turn, to the caller's completion, resulting in declaring replication failure and reporting the failure status to the meta server. The effect of the bug is that the write failure is only discovered when chunk header is read: chunk header checksum mismatch.
Kfs client: deprecate KFS_CLIENT_ environment variable names prefix in favor of QFS_CLIENT_. Honor the variables names with the deprecated prefix if no corresponding QFS_CLIENT_ environment variable set. Do not attempt to load and emit corresponding trace log message if QFS_CLIENT_CONFIG* variable value is an empty string.