tests/063: refine it to test node joining

Signed-off-by: Liu Yuan <namei.unix@gmail.com>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
sheep: update node in cluster driver

When we have update node info in sheep, we also have to update the corresponding
information in the driver, since node join/leave will send the sd nodes in the
corresponding handlers to sheep that will overload the nodes info in sheep.

Signed-off-by: Liu Yuan <namei.unix@gmail.com>
Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>