When metadata is missing don't return a vagrant box with only the name set.

If due to user error a vagrant box does not contain metadata properties (wrong upload, deleted props) searching for a box with the client
(i.e. api/vagrant/vagrant-local/<box-name>) will still return a box with only the name specified for it (no version \ provider) and the client will fail retrieving it.

In this case the box should not be returned.