dog: referencing uninitialized buffer during cluster format

when executing dog cluster format,
by referring to the memory area that is not initialized
update_node_list() was an unintended behavior.

Signed-off-by: Masaki Saeki <saeki.masaki@po.ntts.co.jp>
Signed-off-by: Hitoshi Mitake <mitake.hitoshi@lab.ntt.co.jp>