Moving network_id_from_subnet_id to neutron client

Code for getting network_id from subnet_id is used in several resources.
So function network_id_from_subnet_id should be moved to neutron client
plugin, because it will allow to avoid strange references on
NetworkInterface resource.

Change-Id: I18dfb9a21fdca7a3d047c1cc2e8950bec9622d8c
Merge "Moving network_id_from_subnet_id to neutron client"