KeyValueStore: move buffers from strip_header to BufferTransaction

Signed-off-by: Chendi.Xue <chendi.xue@intel.com>
Merge pull request #2889 from xuechendi/move_buffers_to_BufferTransaction

KeyValueStore: move buffers from strip_header to BufferTransaction

Reviewed-by: Haomai Wang <haomaiwang@gmail.com>