test: fix flaky test-http-set-timeout

Increase timeout on Raspberry Pi to alleviate flakiness.

Fixes: https://github.com/nodejs/node/issues/5854
PR-URL: https://github.com/nodejs/node/pull/5856
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/parallel/test-http-set-timeout.js

@@ -20,7 +20,7 @@ server.listen(common.PORT, function() {
 
   var errorTimer = setTimeout(function() {
     throw new Error('Timeout was not successful');
-  }, 2000);
+  }, common.platformTimeout(2000));
 
   var x = http.get({port: common.PORT, path: '/'});
   x.on('error', function() {