Windows doesn't have 'host' mode networking, so use 'auto'.

That means 'null', not that we can call builder-next on Windows. If and
when we do get builder-next going, this will need to be solved properly
in some way.

Signed-off-by: Paul "TBBle" Hampson <Paul.Hampson@Pobox.com>
Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

builder/builder-next/controller.go

@@ -5,6 +5,7 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
+	"runtime"
 	"time"
 
 	ctd "github.com/containerd/containerd"
@@ -91,6 +92,14 @@ func newSnapshotterController(ctx context.Context, rt http.RoundTripper, opt Opt
 	nc := netproviders.Opt{
 		Mode: "host",
 	}
+
+	// HACK! Windows doesn't have 'host' mode networking.
+	if runtime.GOOS == "windows" {
+		nc = netproviders.Opt{
+			Mode: "auto",
+		}
+	}
+
 	dns := getDNSConfig(opt.DNSConfig)
 
 	wo, err := containerd.NewWorkerOpt(opt.Root, opt.ContainerdAddress, opt.Snapshotter, opt.ContainerdNamespace,