test: skip long path tests on non-Windows

If not running on Windows it skips the long path tests in:

* test-fs-long-path.js
* test-require-long-path.js

Fixes: https://github.com/nodejs/node/issues/2255
PR-URL: https://github.com/nodejs/node/pull/4116


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Minwoo Jung <jmwsoft@gmail.com>