test: use tmpDir instead of fixturesDir

This test was using fixturesDir to create temp files to test. This
patch replaces that with tmpDir and uses `assert` module to test.
Also, this test has been moved to `parallel`, from `sequential` mode.

PR-URL: https://github.com/nodejs/node/pull/2583


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Rich Trott <rtrott@gmail.com>