test: address flaky test-http-client-timeout-event

Use common.platformTimeout() to make test more reliable on Raspberry Pi.

Fixes: #2555
PR-URL: #3968

Reviewed-By: Brendan Ashworth <brendan.ashworth@me.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Roman Klauke <romaaan.git@gmail.com>

test/parallel/test-http-client-timeout-event.js

@@ -33,8 +33,8 @@ server.listen(options.port, options.host, function() {
   setTimeout(function() {
     req.destroy();
     assert.equal(timeout_events, 1);
-  }, 100);
+  }, common.platformTimeout(100));
   setTimeout(function() {
     req.end();
-  }, 50);
+  }, common.platformTimeout(50));
 });