bundles/apt: check for "reboot required" in icinga check only

This avoids the need to manually adjust the status file after a reboot of
the server.

bundles/apt/files/check_unattended_upgrades

@@ -22,12 +22,16 @@ case "$exitcode" in
         exit 1
         ;;
     reboot)
-        echo "Upgrades require a reboot, but automatic rebooting is disabled"
-        exit 1
         ;;
     0)
-        echo "OK"
-        exit 0
+        if [[ -f /var/run/reboot-required ]]
+        then
+            echo "OK, but updates require a reboot"
+            exit 1
+        else
+            echo "OK"
+            exit 0
+        fi
         ;;
     *)
         echo "Last exitcode was $exitcode"