Description of problem:

VirtIO Balloon statistics are not available on Windows 2016.

Version-Release number of selected component (if applicable):
virtio-win-1.9.3-1.el7
qemu-kvm-ev-2.9.0-16.el7_4.5.1.x86_64

How reproducible:
always

Steps to Reproduce:
1. Start QEMU using command line:
/usr/libexec/qemu-kvm -m 2G -device virtio-balloon-pci,id=balloon0 -qmp-pretty stdio /rhev/data-center/mnt/gateway:_home_data_ovirt4.1-data/8791a57e-bac2-45ab-83c1-bb069d41e094/images/04aefbf6-4f32-43fa-8749-b11efd5cf3f5/e1196018-5965-460e-b0e8-92a8d2720cad
2. Enable collection of stats by QMP command:
{ "execute": "qom-set", "arguments": {
  "path": "balloon0",
  "property": "guest-stats-polling-interval",
  "value": 5 } }

3. Check the stats by QMP command:
{ "execute": "qom-get", "arguments": {
  "path": "balloon0",
  "property": "guest-stats"  } }


Actual results:

{ "execute": "qom-get", "arguments": {
  "path": "balloon0",
  "property": "guest-stats"  } }
{
    "return": {
        "stats": {
            "stat-swap-out": -1,
            "stat-available-memory": -1,
            "stat-free-memory": -1,
            "stat-minor-faults": -1,
            "stat-major-faults": -1,
            "stat-total-memory": -1,
            "stat-swap-in": -1
        },
        "last-update": 1506516540
    }
}


Expected results:
There should be values other than -1.