Devices endpoint returns hyphenated field instead of snake_case

According to OpenStack API working group, API response fields are supposed to be snake_case, not hyphenated. We're currently returning a body that looks like:

{"hosts": [...], "network-devices": [...]} from GET /v1/devices. This needs to be changed to use "network_devices" as the field name instead.

https://specs.openstack.org/openstack/api-wg/guidelines/naming.html#fields-in-an-api-request-or-response-body

Example of issue:

$ http http://localhost:8080/v1/devices $CRATON_HTTP_HEADERS
{
    "devices": {
        "hosts": [
            {
                "active": true,
                "cell_id": 1,
                "cloud_id": 1,
                "created_at": "2017-03-22T16:13:58.000000",
                "device_type": "server",
                "id": 2,
                "ip_address": "192.168.1.5",
                "links": [
                    {
                        "href": "http://localhost:8080/v1/network-devices/1",
                        "rel": "up"
                    }
                ],
                "name": "host0.ORD135.C0001.C-1.example1.com",
                "note": null,
                "parent_id": 1,
                "project_id": "6319ff30-52de-4d09-8b21-d53d0054460a",
                "region_id": 1,
                "updated_at": null
            },
            ...
            {
                "active": true,
                "cell_id": 4,
                "cloud_id": 1,
                "created_at": "2017-03-22T16:14:00.000000",
                "device_type": "container",
                "id": 30,
                "ip_address": "172.0.0.14",
                "links": [
                    {
                        "href": "http://localhost:8080/v1/hosts/29",
                        "rel": "up"
                    }
                ],
                "name": "container_host0.DFW.C0002.C-1.example1.com",
                "note": null,
                "parent_id": 29,
                "project_id": "6319ff30-52de-4d09-8b21-d53d0054460a",
                "region_id": 2,
                "updated_at": null
            }
        ],
        "network-devices": [
            {
                "access_secret_id": null,
                "active": true,
                "cell_id": 1,
                "cloud_id": 1,
                "created_at": "2017-03-22T16:13:58.000000",
                "device_type": "switch",
                "id": 1,
                "ip_address": "10.10.1.1",
                "links": [
                    {
                        "href": "http://localhost:8080/v1/cells/1",
                        "rel": "up"
                    }
                ],
                "model_name": "model-x",
                "name": "switch1.C0001.ORD135.example.com",
                "os_version": "version-1",
                "parent_id": null,
                "project_id": "6319ff30-52de-4d09-8b21-d53d0054460a",
                "region_id": 1,
                "updated_at": null,
                "vlans": null
            },
            ...
            {
                "access_secret_id": null,
                "active": true,
                "cell_id": 4,
                "cloud_id": 1,
                "created_at": "2017-03-22T16:14:00.000000",
                "device_type": "switch",
                "id": 28,
                "ip_address": "10.10.1.1",
                "links": [
                    {
                        "href": "http://localhost:8080/v1/cells/4",
                        "rel": "up"
                    }
                ],
                "model_name": "model-x",
                "name": "switch1.C0002.DFW.example.com",
                "os_version": "version-1",
                "parent_id": null,
                "project_id": "6319ff30-52de-4d09-8b21-d53d0054460a",
                "region_id": 2,
                "updated_at": null,
                "vlans": null
            }
        ]
    },
    "links": [
        {
            "href": "http://localhost:8080/v1/devices?resolved-values=True&descendants=False&sort_dir=asc&details=False&limit=30&sort_keys=created_at%2Cid",
            "rel": "first"
        },
        {
            "href": "http://localhost:8080/v1/devices?resolved-values=True&descendants=False&sort_dir=asc&details=False&limit=30&sort_keys=created_at%2Cid",
            "rel": "prev"
        },
        {
            "href": "http://localhost:8080/v1/devices?resolved-values=True&descendants=False&sort_dir=asc&details=False&limit=30&sort_keys=created_at%2Cid",
            "rel": "self"
        },
        {
            "href": "http://localhost:8080/v1/devices?resolved-values=True&descendants=False&sort_dir=asc&marker=30&details=False&limit=30&sort_keys=created_at%2Cid",
            "rel": "next"
        }
    ]
}