[compute] Add list_image_metadata request
[compute] Add list_server_metadata request
[compute] Add set_image_metadata request
[compute] Add set_server_metadata request
[compute] Add update_image_metadata request
[compute] Add update_server_metadata request
Update cassettes

Setup difference used:
  - local devstack
  - different tenant from openstack admin tenant in environment.yml
Merge pull request #72 from alvingarcia/feature/14

Image/Server Metadata