test: fix flaky test-http-client-get-url

Fixed test-http-client-get-url by waiting on HTTP GET
requests to finish before closing the server.

PR-URL: https://github.com/nodejs/node/pull/13516
Fixes: https://github.com/nodejs/node/issues/13507
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>

test/parallel/test-http-client-get-url.js

@@ -25,19 +25,23 @@ const assert = require('assert');
 const http = require('http');
 const url = require('url');
 const URL = url.URL;
+const testPath = '/foo?bar';
 
-const server = http.createServer(common.mustCall(function(req, res) {
+const server = http.createServer(common.mustCall((req, res) => {
   assert.strictEqual('GET', req.method);
-  assert.strictEqual('/foo?bar', req.url);
+  assert.strictEqual(testPath, req.url);
   res.writeHead(200, {'Content-Type': 'text/plain'});
   res.write('hello\n');
   res.end();
-  server.close();
 }, 3));
 
-server.listen(0, function() {
-  const u = `http://127.0.0.1:${this.address().port}/foo?bar`;
-  http.get(u);
-  http.get(url.parse(u));
-  http.get(new URL(u));
-});
+server.listen(0, common.localhostIPv4, common.mustCall(() => {
+  const u = `http://${common.localhostIPv4}:${server.address().port}${testPath}`;
+  http.get(u, common.mustCall(() => {
+    http.get(url.parse(u), common.mustCall(() => {
+      http.get(new URL(u), common.mustCall(() => {
+        server.close();
+      }));
+    }));
+  }));
+}));