Support Keystone AuthN and AuthZ for k8s

[OpenStack Infra]

https://review.openstack.org/633571
Dear bug triager. This bug was created since a commit was marked with DOCIMPACT.
Your project "openstack/magnum" is set up so that we directly report the documentation bugs against it. If this needs changing, the docimpact-group option needs to be added for the project. You can ask the OpenStack infra team (#openstack-infra on freenode) for help if you need to.

commit a7dc26a2b15114698d96aa24d7de1bb46e99e7dd
Author: Feilong Wang <email address hidden>
Date: Mon Dec 3 16:36:23 2018 +1300

    Support Keystone AuthN and AuthZ for k8s

    Now cloud-provider-openstack of Kubernetes has a webhook to support
    Keystone authorization and authentication. With this feature, user
    can use a new label 'keystone-auth-enabled' to enable the keystone
    authN and authZ.

    DocImpact
    Task: 21637
    Story: 1755770

    Change-Id: I3d21ad8f55c0d7308a302f62db9e9af147a604f8
    (cherry picked from commit 59da4e25a6a31e296f8ad734395a791015769424)