benchmark: fix chunky client benchmark execution

This commit fixes a few things for this benchmark:

1. Ensures the temporary directory for the unix socket exists.
2. Prevents the client code from being run directly because the
server script is the one that calls out the client code.
3. Ensures the server is closed once the client benchmarks have
finished.
4. Since this is an http benchmark, it should be moved to the http
benchmarks subdirectory.

PR-URL: https://github.com/iojs/io.js/pull/1257


Reviewed-By: Roman Reiss <me@silverwind.io>