Validate serverURL on Start (#4204)

* Added basic validation of publicServerURL

* Fixed up 'verifyServerUrl' and added tests

* Use Parse.serverURL instead, general cleanup.

* Test server port moved to 13376

* Removed reconfigureServer calls with simple changing of Parse.serverURL

* changed var to const

* Disabled automatic serverURL verification during testing, moved verification call into app.on('mount') callback, removed setTimeout from verification.

spec/ParseServer.spec.js

@@ -0,0 +1,34 @@
+'use strict';
+/* Tests for ParseServer.js */
+const express = require('express');
+
+import ParseServer from '../src/ParseServer';
+
+describe('Server Url Checks', () => {
+
+  const app = express();
+  app.get('/health', function(req, res){
+    res.send('OK');
+  });
+  app.listen(13376);
+
+  it('validate good server url', (done) => {
+    Parse.serverURL = 'http://localhost:13376';
+    ParseServer.verifyServerUrl(function(result) {
+      if(!result) {
+        done.fail('Did not pass valid url');
+      }
+      done();
+    });
+  });
+
+  it('mark bad server url', (done) => {
+    Parse.serverURL = 'notavalidurl';
+    ParseServer.verifyServerUrl(function(result) {
+      if(result) {
+        done.fail('Did not mark invalid url');
+      }
+      done();
+    });
+  });
+});