Fix BadRequest for 'ref' as string value

Before schema validation patch [1] got merged, it was allowed to
pass "ref" as string value (ref:"string") in request body of
snapshot_manage create API but after schema changes, it is
returning 400 error.

This patch fixes this issue by allowing user to pass "ref" parameter
as string.

Note: In case user uses python-cinderclient to manage snapshot, it
always passes "ref" parameter as object (dict).

Change-Id: I6464eacf9f970cbcc1429a50bd59d59faf262bc6
Closes-Bug: #1743338

cinder/api/schemas/snapshot_manage.py

@@ -31,7 +31,7 @@ create = {
                 "metadata": parameter_types.metadata_allows_null,
                 "name": parameter_types.name_allow_zero_min_length,
                 "volume_id": parameter_types.uuid,
-                "ref": {'type': ['object', 'null']},
+                "ref": {'type': ['object', 'null', 'string']},
             },
             'required': ['ref', 'volume_id'],
             'additionalProperties': False,

cinder/tests/unit/api/contrib/test_snapshot_manage.py

@@ -167,6 +167,29 @@ class SnapshotManageTest(test.TestCase):
         # 5th argument of args is metadata.
         self.assertIsNone(args[5])
 
+    @mock.patch('cinder.volume.rpcapi.VolumeAPI.manage_existing_snapshot')
+    @mock.patch('cinder.volume.api.API.create_snapshot_in_db')
+    @mock.patch('cinder.db.sqlalchemy.api.service_get')
+    def test_manage_snapshot_ok_ref_as_string(self, mock_db,
+                                              mock_create_snapshot,
+                                              mock_rpcapi):
+
+        mock_db.return_value = fake_service.fake_service_obj(
+            self._admin_ctxt,
+            binary=constants.VOLUME_BINARY)
+
+        body = {'snapshot': {'volume_id': fake.VOLUME_ID,
+                             'ref': "string"}}
+
+        res = self._get_resp_post(body)
+        self.assertEqual(http_client.ACCEPTED, res.status_int, res)
+
+        # Check the volume_rpcapi.manage_existing_snapshot was called with
+        # correct arguments.
+        self.assertEqual(1, mock_rpcapi.call_count)
+        args = mock_rpcapi.call_args[0]
+        self.assertEqual(body['snapshot']['ref'], args[2])
+
     @mock.patch('cinder.objects.service.Service.is_up',
                 return_value=True,
                 new_callable=mock.PropertyMock)