Automatic merge from submit-queue

openstack: Implement the `Routes` provider API

``` release-note

Implement the Routes provider API for OpenStack using Neutron extraroute extension.  This removes the need for flannel/etc where supported.  To use, ensure all your nodes are on the same Neutron (private) network and specify the router ID in new `[Route]` section of provider config:

    [Route]
    router-id = <router UUID>
```