[#70443650] Replace deprecated get_network call

The Fog request layer method get_network has been deprecated in favour of get_network_complete, as per https://github.com/fog/fog/pull/2683

This PR replaces the use of get_network with get_network_complete, and bumps the version accordingly.

The Core::OrgVdcNetwork#vcloud_attributes method response changes as a result. This has minimal impact at the moment, bar tandem changes needed in the integration tests for http://github.com/alphagov/vcloud-net_launcher