add live_system config option

This is to be used in environments where reboot is strictly unneeded;
such as when building packages in a chroot

bin/sau

@@ -115,6 +115,9 @@ def main():
         log.error(f'Upgrade failed: {e}')
         return 1
 
+    if not conf.getboolean('default', 'live_system', True):
+        return 0
+
     if conf.getboolean('default', 'do_service_restart', fallback=True):
         reboot_recommended = sau.services.restart_services()