Change test cases port to be dynamic

To avoid port collision when running in Jenkins

test/executor.test.js

@@ -38,7 +38,7 @@ describe('executor', function() {
 
   var dummyInstructions = someInstructions({
     config: {
-      port: 3000,
+      port: 0,
       host: '127.0.0.1',
       restApiRoot: '/rest-api',
       foo: { bar: 'bat' },

test/fixtures/env-app/config.json

@@ -1,4 +1,4 @@
 {
-  "port": 3000,
+  "port": 0,
   "host": "127.0.0.1"
 }

test/fixtures/simple-app/config.json

@@ -1,4 +1,4 @@
 {
-  "port": 3000,
+  "port": 0,
   "host": "127.0.0.1"
 }