Make app.models unique per app instance

Remove a source of confusion in unit-tests.

lib/loopback.js

@@ -57,6 +57,11 @@ function createApplication() {
 
   utils.merge(app, proto);
 
+  // Create a new instance of models registry per each app instance
+  app.models = function() {
+    return proto.models.apply(this, arguments);
+  };
+
   return app;
 }
 

test/app.test.js

@@ -76,6 +76,15 @@ describe('app', function() {
     });
   });
 
+  describe('app.models', function() {
+    it('is unique per app instance', function() {
+      var Color = app.model('Color', { dataSource: 'db' });
+      expect(app.models.Color).to.equal(Color);
+      var anotherApp = loopback();
+      expect(anotherApp.models.Color).to.equal(undefined);
+    });
+  });
+
   describe('app.boot([options])', function () {
     beforeEach(function () {
       app.boot({