Use 'openstack subnet list' to replace 'nova network-list'
Use 'openstack subnet list' to replace 'nova network-list'

The command "nova network-list" is deprecated and will be removed
after Nova 15.0.0 is released, and the chapter want to get IP ranges,
So this patch use 'openstack subnet list' to replace it.

partial-implements: blueprint use-openstack-command

Change-Id: Id0074c4274b9e27269b9f96c89f073bfa5225ed1

openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals