cron: add @service which is probably clearer than @reboot in app context

src/scheduler.js

@@ -73,7 +73,7 @@ async function createJobs(app, schedulerConfig) {
         debug(`createJobs: ${taskName} (${app.fqdn}) will run in container ${containerName}`);
 
         let cronTime;
-        if (schedule === '@reboot') {
+        if (schedule === '@service') {
             cronTime = new Date(Date.now() + 2*1000); // 2 seconds from now
         } else {
             // random is so that all crons start at once to decrease memory pressure