Set application's id property only if it's empty.

Fix `Application.resetKeys()` to reset instance id only if it is not
already set. This fixes a bug where each call of resetKeys created
a new instance.

common/models/application.js

@@ -92,7 +92,9 @@ module.exports = function(Application) {
 
     var app = ctx.instance;
     app.created = app.modified = new Date();
+    if (!app.id) {
       app.id = generateKey('id', 'md5');
+    }
     app.clientKey = generateKey('client');
     app.javaScriptKey = generateKey('javaScript');
     app.restApiKey = generateKey('restApi');

test/model.application.test.js

@@ -174,6 +174,30 @@ describe('Application', function() {
     });
   });
 
+  it('Reset keys without create a new instance', function(done) {
+    Application.resetKeys(registeredApp.id, function(err, result) {
+      var app = result;
+      assert(app.id);
+      assert(app.id === registeredApp.id);
+      registeredApp = app;
+      done(err, result);
+    });
+  });
+
+  it('Reset keys without create a new instance - promise variant', function(done) {
+    Application.resetKeys(registeredApp.id)
+    .then(function(result) {
+      var app = result;
+      assert(app.id);
+      assert(app.id === registeredApp.id);
+      registeredApp = app;
+      done();
+    })
+    .catch(function(err) {
+      done(err);
+    });
+  });
+
   it('Authenticate with application id & clientKey', function(done) {
     Application.authenticate(registeredApp.id, registeredApp.clientKey,
       function(err, result) {