windows: The DefaultSpec platform should match the Default matcher

The Windows Default matcher also checks the the OS Version prefix,
however, the platforms.DefaultSpec does not include it, which means
that it won't match the matcher.

This solves the issue by adding the OS Version to the DefaultSpec.

Signed-off-by: Claudiu Belu <cbelu@cloudbasesolutions.com>

platforms/defaults_windows_test.go

@@ -17,13 +17,36 @@
 package platforms
 
 import (
+	"fmt"
+	"reflect"
+	"runtime"
 	"sort"
 	"testing"
 
 	imagespec "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/stretchr/testify/assert"
+	"golang.org/x/sys/windows"
 )
 
+func TestDefault(t *testing.T) {
+	major, minor, build := windows.RtlGetNtVersionNumbers()
+	expected := imagespec.Platform{
+		OS:           runtime.GOOS,
+		Architecture: runtime.GOARCH,
+		OSVersion:    fmt.Sprintf("%d.%d.%d", major, minor, build),
+		Variant:      cpuVariant(),
+	}
+	p := DefaultSpec()
+	if !reflect.DeepEqual(p, expected) {
+		t.Fatalf("default platform not as expected: %#v != %#v", p, expected)
+	}
+
+	s := DefaultString()
+	if s != Format(p) {
+		t.Fatalf("default specifier should match formatted default spec: %v != %v", s, p)
+	}
+}
+
 func TestMatchComparerMatch(t *testing.T) {
 	m := matchComparer{
 		defaults: Only(imagespec.Platform{
@@ -36,6 +59,10 @@ func TestMatchComparerMatch(t *testing.T) {
 		platform imagespec.Platform
 		match    bool
 	}{
+		{
+			platform: DefaultSpec(),
+			match:    true,
+		},
 		{
 			platform: imagespec.Platform{
 				Architecture: "amd64",