lib/option: support 'B' notation for byte

Signed-off-by: Liu Yuan <namei.unix@gmail.com>
sheep/recovery: don't recover object from stale dir with invalid epoch

Signed-off-by: Liu Yuan <namei.unix@gmail.com>
erasure code: make data stripe size as 512 Byte

Signed-off-by: Liu Yuan <namei.unix@gmail.com>