Tests: reworked http SSL tests to use IO::Socket::SSL. Relevant infrastructure is provided in Test::Nginx http() functions. This also ensures that SSL handshake and various read and write operations are guarded with timeouts. The ssl_sni_reneg.t test uses IO::Socket::SSL::_get_ssl_object() to access the Net::SSLeay object directly and trigger renegotation. While not exactly correct, this seems to be good enough for tests. Similarly, IO::Socket::SSL::_get_ssl_object() is used in ssl_stapling.t, since SSL_ocsp_staple_callback is called with the socket instead of the Net::SSLeay object. Similarly, IO::Socket::SSL::_get_ssl_object() is used in ssl_verify_client.t, since there seems to be no way to obtain CA list with IO::Socket::SSL. Notable change to http() request interface is that http_end() now closes the socket. This is to make sure that SSL connections are properly closed and SSL sessions are not removed from the IO::Socket::SSL session cache. This affected access_log.t, which was modified accordingly.