Limit functionality only partially implemented for listing hosts

[git-harry]

The ('hosts', 'GET') schema advertises support for limiting the number of returned results [1]. There are also references to this in other parts of the code and the documentation. It appears this functionality has only been partially implemented, there is no where the limit is actually used. Depending on the priority of the ability to limit the results returned this feature should either be fixed or removed to prevent confusion and properly implemented at a later date.

Example of attempted use of limit:
```
curl "http://172.17.0.02:8080/v1/hosts?region_id=1&limit=1" -H "Content-Type: application/json" -H "X-Auth-Token: demo" -H "X-Auth-User: demo" -H "X-Auth-Project: b9f10eca66ac4c279c139d01e65f96b4" -s | python -m json.tool | head -n30
[
    {
        "active": true,
        "cell_id": 1,
        "device_type": "server",
        "id": 2,
        "ip_address": "192.168.1.5",
        "name": "host0.ORD135.C0001.C-1.example1.com",
        "note": null,
        "parent_id": null,
        "region_id": 1
    },
    {
        "active": true,
        "cell_id": 1,
        "device_type": "server",
        "id": 4,
        "ip_address": "192.168.1.7",
        "name": "host0.ORD135.C0001.C-2.example2.com",
        "note": null,
        "parent_id": null,
        "region_id": 1
    },
    {
        "active": true,
        "cell_id": 2,
        "device_type": "server",
        "id": 7,
        "ip_address": "192.168.1.9",
        "name": "host0.ORD135.C0002.C-1.example1.com",
```

[1] https://github.com/openstack/craton/blob/master/craton/api/v1/schemas.py#L362