add disk usage task

src/taskworker.js

@@ -15,6 +15,7 @@ const apptask = require('./apptask.js'),
     reverseProxy = require('./reverseproxy.js'),
     safe = require('safetydance'),
     settings = require('./settings.js'),
+    system = require('./system.js'),
     tasks = require('./tasks.js'),
     updater = require('./updater.js');
 
@@ -28,6 +29,7 @@ const TASKS = { // indexed by task type
     syncExternalLdap: externalLdap.sync,
     changeMailLocation: mail.changeLocation,
     syncDnsRecords: dns.syncDnsRecords,
+    updateDiskUsage: system.updateDiskUsage,
 
     _identity: async (arg, progressCallback) => { progressCallback(); return arg; },
     _error: async (arg, progressCallback) => { progressCallback(); throw new Error(`Failed for arg: ${arg}`); },