[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
[vcloud_director] Implement get_thumbnail request.
[vcloud_director] Documentation fixes.
[vcloud_director] Mocking for vDC storage profiles.
Merge pull request #2253 from nosborn/vcloud_director_storage_class

[vcloud_director] Mocking for vDC storage profiles.
[vcloud_director] Expose URLs in method docs.
[vcloud_director] Add post_instantiate_vapp_template request.
Merge pull request #2255 from nosborn/vcloud_director_instantiate_vapp_template

[vcloud_director] Add post_instantiate_vapp_template request.
Auto-merge remote-tracking branch 'upstream/master'