Auto-Generate SSH Key when one isn't provided

[iancward]

The kitchen-ec2 driver provides the capability to auto-generate an SSH key when one is not provided; it would be good if this driver could do the same.
The primary purpose of this is to use test kitchen in a CI/CD environment where the runners are shared and we don't have a way to provide a private key on disk.

It looks like the openstack API has a method to create SSH keys, so I imagine this would be technically feasible.
https://developer.openstack.org/api-ref/compute/?expanded=create-or-import-keypair-detail#keypairs-keypairs