Create for cluster failed: Unknown attribute for argument cluster: labels (HTTP 400)

I'm evaluating magnum, and found that vanilla devstack installation for pike fails on cluster-create command with message Create for cluster foobar failed: Unknown attribute for argument cluster: labels (HTTP 400)

Steps to reproduce:

devstack, stable/pike branch
local.conf:
[[local|localrc]]
ADMIN_PASSWORD=sacred
DATABASE_PASSWORD=$ADMIN_PASSWORD
RABBIT_PASSWORD=$ADMIN_PASSWORD
SERVICE_PASSWORD=$ADMIN_PASSWORD
enable_plugin heat https://github.com/openstack/heat stable/pike
enable_plugin magnum https://github.com/openstack/magnum stable/pike

source openrc
magnum cluster-template-create k8s-cluster-template --image 57af817a-5ead-4352-be2b-9e84d73969c8 --keypair x220 --external-network 7877b03e-ed18-4733-8ccb-2d7a1338ffbb --dns-nameserver 8.8.8.8 --flavor m1.small --coe kubernetes --network-driver flannel

(image - fedora-atomic, external-network - public network).

magnum cluster-create --cluster-template 282b0792-692c-4874-8ab0-e54053e7f5d2 foobar

Create for cluster foobar failed: Unknown attribute for argument cluster: labels (HTTP 400) (Request-ID: req-b47a0fa2-2dc5-4b7f-89d9-7cd044f8aa13)

Log entry from magnum-api:

Oct 10 13:44:12 devstack magnum-api[16595]: 2017-10-10 13:44:12.191 DEBUG magnum.api.controllers.v1 [-] Processing request: url: http://78.140.148.46:9511/v1/clusters, POST, body: {"cluster_template_id": "282b0792-692c-4874-8ab0-e54053e7f5d2", "na
me": "foobar", "labels": {}, "keypair": null, "master_count": 1, "node_count": 1, "create_timeout": 60, "discovery_url": null} from (pid=27420) _route /opt/stack/magnum/magnum/api/controllers/v1/__init__.py:233
Oct 10 13:44:12 devstack magnum-api[16595]: 2017-10-10 13:44:12.194 DEBUG oslo_policy._cache_handler [req-a25b98ef-ace5-403b-bd72-883544462864 demo demo] Reloading cached file /etc/magnum/policy.json from (pid=27420) read_cached_
file /usr/local/lib/python2.7/dist-packages/oslo_policy/_cache_handler.py:40
Oct 10 13:44:12 devstack magnum-api[16595]: 2017-10-10 13:44:12.197 DEBUG oslo_policy.policy [req-a25b98ef-ace5-403b-bd72-883544462864 demo demo] Reloaded policy file: /etc/magnum/policy.json from (pid=27420) _load_policy_file /u
sr/local/lib/python2.7/dist-packages/oslo_policy/policy.py:681
Oct 10 13:44:12 devstack magnum-api[16595]: 2017-10-10 13:44:12.200 DEBUG wsme.api [req-a25b98ef-ace5-403b-bd72-883544462864 demo demo] Client-side error: Unknown attribute for argument cluster: labels from (pid=27420) format_exc
eption /usr/local/lib/python2.7/dist-packages/wsme/api.py:222
Oct 10 13:44:12 devstack magnum-api[16595]: 2017-10-10 13:44:12.201 INFO werkzeug [req-a25b98ef-ace5-403b-bd72-883544462864 demo demo] 78.140.148.46 - - [10/Oct/2017 13:44:12] "POST /v1/clusters HTTP/1.1" 400 -

devstack commit: 4358418d7d20a18667801105eb246199036e9d57 (stable/pike)
magnum commit: 133352d3bb06a35d77187f7bad56ae47eb324815 (stable/pile)