apptask: set the memory limit based on the backup config

fixes #759

src/apptaskmanager.js

@@ -37,9 +37,10 @@ function initializeSync() {
 }
 
 // callback is called when task is finished
-function scheduleTask(appId, taskId, callback) {
+function scheduleTask(appId, taskId, options, callback) {
     assert.strictEqual(typeof appId, 'string');
     assert.strictEqual(typeof taskId, 'string');
+    assert.strictEqual(typeof options, 'object');
     assert.strictEqual(typeof callback, 'function');
 
     if (!gInitialized) initializeSync();
@@ -72,8 +73,7 @@ function scheduleTask(appId, taskId, callback) {
 
     scheduler.suspendJobs(appId);
 
-    // TODO: set memory limit for app backup task
-    tasks.startTask(taskId, { logFile, timeout: 20 * 60 * 60 * 1000 /* 20 hours */, nice: 15 }, function (error, result) {
+    tasks.startTask(taskId, Object.assign(options, { logFile }), function (error, result) {
         callback(error, result);
 
         delete gActiveTasks[appId];