scheduler: suspend/resume jobs when apptask is active

the cron job container was holding on to the volume any container changes.

src/scheduler.js

@@ -1,7 +1,9 @@
 'use strict';
 
 exports = module.exports = {
-    sync: sync
+    sync,
+    suspendJobs,
+    resumeJobs
 };
 
 let apps = require('./apps.js'),
@@ -15,8 +17,18 @@ let apps = require('./apps.js'),
     _ = require('underscore');
 
 // appId -> { containerId, schedulerConfig (manifest), cronjobs }
-var gState = { };
+let gState = { };
+let gSuspendedAppIds = new Set(); // suspended because some apptask is running
 
+function suspendJobs(appId) {
+    debug(`suspendJobs: ${appId}`);
+    gSuspendedAppIds.add(appId);
+}
+
+function resumeJobs(appId) {
+    debug(`resumeJobs: ${appId}`);
+    gSuspendedAppIds.delete(appId);
+}
 
 function runTask(appId, taskName, callback) {
     assert.strictEqual(typeof appId, 'string');
@@ -26,6 +38,8 @@ function runTask(appId, taskName, callback) {
     const JOB_MAX_TIME = 30 * 60 * 1000; // 30 minutes
     const containerName = `${appId}-${taskName}`;
 
+    if (gSuspendedAppIds.has(appId)) return callback();
+
     apps.get(appId, function (error, app) {
         if (error) return callback(error);