[vcloud_director] Add get_network_complete non-lossy API request.

The existing get_network request uses a parser that translates the XML from vCloud Director into ruby-style snake case data structures, but unfortunately loses some information along the way.

This PR adds a 'get_network_complete' method that just uses the general purpose ToHashDocument parser, and so preserves the entire body.

This also enables loading this content directly into post_create_org_vdc_network, as suggested by the API docs.