Glance returned 200 status code when we add element to nonexistent property

[Darja Shakhray]

ENVIRONMENT: devstack, Glance (master, 14.08.2015)

STEPS TO REPRODUCE:
We tried add element to nonexistent property on artifact.
Send request
curl -H "X-Auth-Token: b582b953413b4a8896bfa27e1b70d4e0" -H "Content-Type:application/json" -X PATCH -d '[{"op": "add", "path": "/banana", "value": "minion_Stuart"}]' http://172.18.76.44:9292/v3/artifacts/myartifact/v2.0/4d1e26e5-87b7-49b4-99bd-0e6232a80142 -i

EXPECTED RESULT:
status code 400 and error description

ACTUAL RESULT:
HTTP/1.1 200 OK
Content-Length: 517
Content-Type: application/json; charset=UTF-8
X-Openstack-Request-Id: req-req-efd101f6-7dd4-4a97-95f6-d647a7e21cb7
Date: Mon, 17 Aug 2015 06:55:46 GMT

{"description": null, "published_at": null, "tags": [], "depends_on": null, "created_at": "2015-08-14T13:42:13.000000", "type_name": "MyArtifact", "updated_at": "2015-08-14T14:10:17.000000", "visibility": "public", "id": "4d1e26e5-87b7-49b4-99bd-0e6232a80142", "type_version": "2.0", "state": "creating", "version": "12.0.0", "references": [], "prop1": null, "prop2": null, "owner": "b230d6ea1098462bb98d993b9cf386c0", "image_file": null, "deleted_at": null, "screenshots": [], "int_list": null, "name": "artifact-3"}