kern/lockdown: Set a variable if the GRUB is locked down

It may be useful for scripts to determine whether the GRUB is locked
down or not. Add the lockdown variable which is set to "y" when the GRUB
is locked down.

Suggested-by: Dimitri John Ledkov <xnox@ubuntu.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/kern/lockdown.c

@@ -18,6 +18,7 @@
  */
 
 #include <grub/dl.h>
+#include <grub/env.h>
 #include <grub/file.h>
 #include <grub/lockdown.h>
 #include <grub/verify.h>
@@ -71,6 +72,9 @@ grub_lockdown (void)
   lockdown = GRUB_LOCKDOWN_ENABLED;
 
   grub_verifier_register (&lockdown_verifier);
+
+  grub_env_set ("lockdown", "y");
+  grub_env_export ("lockdown");
 }
 
 int