Fix incorrect usage of `app` in app.test.js

The `beforeEach` hook was using a local `var app`, the test was
accessing global `app` created by `test/support.js`.

test/app.test.js

@@ -78,8 +78,6 @@ describe('app', function() {
 
   describe('app.boot([options])', function () {
     beforeEach(function () {
-      var app = this.app = loopback();
-
       app.boot({
         app: {
           port: 3000, 

test/support.js

@@ -17,7 +17,7 @@ request = require('supertest');
 loopback.User.settings.saltWorkFactor = 4;
 
 beforeEach(function () {
-  app = loopback();
+  this.app = app = loopback();
 
   // setup default data sources
   loopback.setDefaultDataSourceForType('db', {