TT#115300 GRUB templates: just exit for boot from next device

This pretty much never works for me, while exiting GRUB switches to the
next device in the boot order, so let's just "exit" GRUB and name the
menu entries accordingly.

This is taken over from upstream change
89c43982fb

Change-Id: I23106b202bfc57f3173cb1ee0326c5b7eddd0474

templates/boot/grub/addons.cfg

@@ -17,9 +17,8 @@ submenu "Addons ->" --class=submenu {
       fi
   }
 
-  menuentry "Boot OS of first partition on first disk" {
-      set root=(hd0,1)
-      chainloader +1
+  menuentry "Boot from next device" {
+      exit
   }
 
 }