Comment 3 for bug 2044403

`"allow_dns": false` and `"dns_servers": []` are properly reflected in maas machine read.

        {
            "type": "physical",
            "link_speed": 0,
            "mac_address": "52:54:00:a9:02:e4",
            "vendor": "Red Hat, Inc.",
            "links": [
                {
                    "id": 133,
                    "mode": "auto",
                    "ip_address": "192.168.152.101",
                    "subnet": {
                        "name": "192.168.152.0/24",
                        "description": "",
                        "vlan": {
                            "vid": 152,
                            "mtu": 1500,
                            "dhcp_on": false,
                            "external_dhcp": null,
                            "relay_vlan": null,
                            "secondary_rack": null,
                            "id": 13,
                            "primary_rack": null,
                            "name": "152",
                            "space": "space-isolated",
                            "fabric": "fabric-1",
                            "fabric_id": 1,
                            "resource_uri": "/MAAS/api/2.0/vlans/13/"
                        },
                        "cidr": "192.168.152.0/24",
                        "rdns_mode": 2,
                        "gateway_ip": null,
                        "dns_servers": [],
                        "allow_dns": false,
                        "allow_proxy": true,
                        "active_discovery": false,
                        "managed": true,
                        "disabled_boot_architectures": [],
                        "id": 6,
                        "space": "space-isolated",
                        "resource_uri": "/MAAS/api/2.0/subnets/6/"
                    }