Fix chassis printing for multi node
Fix chassis printing for multi node

Fix chassis __str__() method

Change-Id: If6fb6e3ca51c9942bff36b08c27a9fbde1dc8ca0

FrankDuan/df_code,openstack/dragonflow,openstack/dragonflow,openstack/dragonflow,FrankDuan/df_code,FrankDuan/df_code