LCOW: Don't block export

Signed-off-by: John Howard <jhoward@microsoft.com>

daemon/export.go

@@ -13,15 +13,15 @@ import (
 // ContainerExport writes the contents of the container to the given
 // writer. An error is returned if the container cannot be found.
 func (daemon *Daemon) ContainerExport(name string, out io.Writer) error {
-	if runtime.GOOS == "windows" {
-		return fmt.Errorf("the daemon on this platform does not support export of a container")
-	}
-
 	container, err := daemon.GetContainer(name)
 	if err != nil {
 		return err
 	}
 
+	if runtime.GOOS == "windows" && container.Platform == "windows" {
+		return fmt.Errorf("the daemon on this platform does not support exporting Windows containers")
+	}
+
 	data, err := daemon.containerExport(container)
 	if err != nil {
 		return fmt.Errorf("Error exporting container %s: %v", name, err)