bundles/apt: add flag to disable automatic rebooting

bundles/apt/files/check_unattended_upgrades

@@ -21,6 +21,10 @@ case "$exitcode" in
         echo "Upgrades skipped due to active SSH login"
         exit 1
         ;;
+    reboot)
+        echo "Upgrades require a reboot, but automatic rebooting is disabled"
+        exit 1
+        ;;
     0)
         echo "OK"
         exit 0