[#70499754] Vcloud::Core:Vdc integration tests & related bug fix

Largely adding integration tests to demonstrate the behaviour of the Core::Vdc API, but in the process discovered that #vcloud_attributes and #name were not working (see 3e6bf27). This was caused by an oversight when FogFacade was created, indicating that we are not using Vdc#name or Vdc#vcloud_attributes in Vcloud Tools.

(NB: we do use Vcloud::Fog::ServiceInterface#vdc, in my opinion we should refactor that out rather than ditching Vdc methods.)