refactor(endpoints/api/repository*): added in pre_oci_model abstraction

this is a part of getting ready for oci stuff

[TESTING->using new PR stack]

Issue: https://coreosdev.atlassian.net/browse/QUAY-633

- [ ] It works!
- [ ] Comments provide sufficient explanations for the next contributor
- [ ] Tests cover changes and corner cases
- [ ] Follows Quay syntax patterns and format

endpoints/api/test/test_repository.py

@@ -38,8 +38,8 @@ NOT_FOUND_RESPONSE = {
 ])
 def test_post_changetrust(trust_enabled, repo_found, expected_body, expected_status, client):
   with patch('endpoints.api.repository.tuf_metadata_api') as mock_tuf:
-    with patch('endpoints.api.repository.model') as mock_model:
-      mock_model.repository.get_repository.return_value = MagicMock() if repo_found else None
+    with patch('endpoints.api.repository_models_pre_oci.model.repository.get_repository') as mock_model:
+      mock_model.return_value = MagicMock() if repo_found else None
       mock_tuf.get_default_tags_with_expiration.return_value = ['tags', 'expiration']
       with client_with_identity('devtable', client) as cl:
         params = {'repository': 'devtable/repo'}