[vcloud_director] Supply xmlns with request bodies.
[vcloud_director] Improve tests.
[vcloud_director] Add post/put metadata methods.
[vcloud_director] get_edge_gateways -> get_org_vdc_networks
[vcloud_director] Make get_edge_gateway idempotent.
[vcloud_director] Really make GET requests idempotent.
[vcloud_director|tests] Mark media tests pending when mocking.

Need support for mocking tasks now.
Merge pull request #2252 from nosborn/vcloud_director_xmlns

Vcloud director xmlns