Properly terminate the script.

www/swreg/callhome.php

@@ -81,4 +81,7 @@ if ($row['should_re_ztp'] == 1) {
     } catch (PDOException $e) {
         $logger->crit("Failed to reset re-ZTP bit for {$sn}: {$e->getMessage()}");
     }
+    exit(0);
 }
+
+echo "!\r\n";