Revert "flask-pypy: Remove gunicorn."

This reverts commit c2fe5ff786544a0ede3dd785fecdacd209c49640.
Remove server-tornado.
Remove "gunicorn" from benchmark_config
Merge branch 'revert-pypy-gunicorn' of http://github.com/methane/FrameworkBenchmarks into 896
896 removed tornado option

Running the pypy test for flask with
the tornado option causes it to fail.
Merge branch '896'