cloudron.runSystemChecks should take a callback

src/cloudron.js

@@ -153,14 +153,14 @@ function isRebootRequired(callback) {
 }
 
 // called from cron.js
-function runSystemChecks() {
+function runSystemChecks(callback) {
+    assert.strictEqual(typeof callback, 'function');
+
     async.parallel([
         checkBackupConfiguration,
         checkMailStatus,
         checkRebootRequired
-    ], function (error) {
-        debug('runSystemChecks: done', error);
-    });
+    ], callback);
 }
 
 function checkBackupConfiguration(callback) {