Test with vcloud

The terremark "vcloud" service (https://github.com/fog/fog-terremark/blob/master/lib/fog/terremark/vcloud.rb) includes important utility methods that aren't in the "vanilla" compute service (https://github.com/fog/fog-terremark/blob/master/lib/fog/compute/terremark.rb). Initializing the terremark compute service the way it is done in the existing test will fail on all requests because it will not include the logic in the vcloud service. ex:
```
describe Fog::Compute::Terremark do
  it 'gets a login token' do
    service = Fog::Compute::Terremark.new(
        :terremark_vcloud_username => 'test@example.com',
        :terremark_vcloud_password => '123456')
    service.send(:auth_token)
  end
end
```
will raise `undefined method `request' for nil:NilClass` (referring to the connection property defined in the vcloud service).

This test reflects usage that will succeed in making requests. Should an additional issue be opened to migrate the vcloud utility methods to the terremark service? (here maybe https://github.com/fog/fog-terremark/blob/master/lib/fog/compute/terremark/common.rb) 

This test also mocks the excon requests.