test: use random ports where possible

This helps to prevent issues where a failed test can keep a bound
socket open long enough to cause other tests to fail with EADDRINUSE
because the same port number is used.

PR-URL: https://github.com/nodejs/node/pull/7045
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Rod Vagg <rod@vagg.org>

test/parallel/test-https-byteswritten.js

@@ -27,9 +27,9 @@ var httpsServer = https.createServer(options, function(req, res) {
   res.end(body);
 });
 
-httpsServer.listen(common.PORT, function() {
+httpsServer.listen(0, function() {
   https.get({
-    port: common.PORT,
+    port: this.address().port,
     rejectUnauthorized: false
   });
 });