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.go

@@ -27,6 +27,18 @@ import (
 	"golang.org/x/sys/windows"
 )
 
+// DefaultSpec returns the current platform's default platform specification.
+func DefaultSpec() specs.Platform {
+	major, minor, build := windows.RtlGetNtVersionNumbers()
+	return specs.Platform{
+		OS:           runtime.GOOS,
+		Architecture: runtime.GOARCH,
+		OSVersion:    fmt.Sprintf("%d.%d.%d", major, minor, build),
+		// The Variant field will be empty if arch != ARM.
+		Variant: cpuVariant(),
+	}
+}
+
 type matchComparer struct {
 	defaults        Matcher
 	osVersionPrefix string