Revert "Try to remove the promise"

This reverts commit 5f101ed.

Author: NullVoxPopuli

addon-test-support/-private/ember-exam-test-loader.js

@@ -60,7 +60,7 @@ export default class EmberExamTestLoader extends TestLoader {
    *
    * @method loadModules
    */
-  loadModules({ availableModules } = {}) {
+  async loadModules({ availableModules } = {}) {
     const loadBalance = this._urlParams.get('loadBalance');
     const browserId = this._urlParams.get('browser');
     const modulePath = this._urlParams.get('modulePath');
@@ -119,7 +119,8 @@ export default class EmberExamTestLoader extends TestLoader {
       );
 
       if (this._availableModules) {
-        return this.loadAvailableModules();
+        await this.loadAvailableModules();
+        return;
       }
 
       /**