librados: copy out data to users' buffer for xio

librados: copy out data to users' buffer for xio

rados_aio_read(buf) call objecter->read(). Upon receiving
reply from osd, message->claim_data() is called which
enforces *deep* copy (both bufferlist and data buffers)
because Accelio's registered buffers is NON_SHAREABLE.
Received data is on new bufferlist and buffers but not
in original buffer provided by rados_aio_read() caller.
Another copy to users' buffer is needed

Signed-off-by: Vu Pham <vu@mellanox.com>