rally/samples/deployments/for_deploying_openstack_with_rally/devstack-in-existing-servers.json

{
    "type": "DevstackEngine",
    "devstack_repo": "https://git.openstack.org/openstack-dev/devstack",
    "devstack_branch": "master",
    "provider": {
        "type": "ExistingServers",
        "credentials": [{"user": "root", "host": "10.2.0.8"}]
    }
}