libceph: print fsid and epoch with osd id

Print fsid and epoch in libceph log messages to distinct from which
each message come.

[ idryomov: don't bother with gid for now, print epoch instead ]

Signed-off-by: Satoru Takeuchi <satoru.takeuchi@gmail.com>
Signed-off-by: Daichi Mukai <daichi-mukai@cybozu.co.jp>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>