[WIP][ticket/11016] Use builtin webserver for functional tests

While this works correctly there is a test failure for the authentication test. It appears the PHP webserver doesn't like multiple Cookie headers, but wants them to be listed in a single header. At the same time guzzle (http client lib in goutte) doesn't support enumerating cookies in a single header that way. So we'll have to fix either one of those and probably mark the test incomplete until then.

http://tracker.phpbb.com/browse/PHPBB3-11016