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>
```
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