Return most specific error instead of 404

Particularly for client-side errors, we ought to at least return the
actual error status instead of a generic 404.

Enablement of negative Tempest tests.

Change-Id: Ieaf658c9bd202dbb5000c10c43bdd1afa15a2aa1

mixmatch/proxy.py

@@ -12,6 +12,8 @@
 #   License for the specific language governing permissions and limitations
 #   under the License.
 
+import collections
+import six
 import requests
 import flask
 
@@ -231,21 +233,33 @@ class RequestHandler(object):
         if not CONF.search_by_broadcast:
             return self._local_forward()
 
+        errors = collections.defaultdict(lambda: [])
         for sp in self.enabled_sps:
             if sp == 'default':
                 response = self._do_request_on('default')
                 if 200 <= response.status_code < 300:
                     return self._finalize(response)
+                else:
+                    errors[response.status_code].append(response)
             else:
                 self.service_provider = sp
                 for p in auth.get_projects_at_sp(sp, self.details['token']):
                     response = self._do_request_on(sp, p)
                     if 200 <= response.status_code < 300:
                         return self._finalize(response)
-        return flask.Response(
-            "Not found\n.",
-            404
-        )
+                    else:
+                        errors[response.status_code].append(response)
+
+        if six.viewkeys(errors) == {404}:
+            return self._finalize(errors[404][0])
+        else:
+            utils.safe_pop(errors, 404)
+
+        if len(errors.keys()) == 1:
+            return self._finalize(list(errors.values())[0][0])
+
+        # TODO(jfreud): log
+        return flask.Response("Something strange happened.\n", 500)
 
     def _aggregate_forward(self):
         if not CONF.aggregation:

mixmatch/tests/functional/tempest_blacklist.txt

@@ -1,5 +1,3 @@
-negative
-Negative
 tempest.api.image.admin.v2.test_images.BasicAdminOperationsImagesTest.test_admin_deactivate_reactivate_image
 tempest.api.image.v2.test_images_metadefs_namespaces.MetadataNamespacesTest.test_basic_metadata_definition_namespaces
 tempest.api.volume.admin.v3.test_user_messages.UserMessagesTest.test_delete_message

mixmatch/tests/unit/test_images.py

@@ -167,7 +167,7 @@ class TestImages(base.BaseTest):
             headers=self.auth.get_headers()
         )
 
-        self.assertEqual(response.status_code, 404)
+        self.assertEqual(response.status_code, 500)
 
     def test_list_images(self):
         self.requests_fixture.get(