SSL: do not treat SSL handshake as request.

SSL: do not treat SSL handshake as request.

The request object will not be created until SSL handshake is complete.
This simplifies adding another connection handler that does not need
request object right after handshake (e.g., SPDY).

There are also a few more intentional effects:

 - the "client_header_buffer_size" directive will be taken from the
   server configuration that was negotiated by SNI;

 - SSL handshake errors and timeouts are not logged into access log
   as bad requests;

 - ngx_ssl_create_connection() is not called until the first byte of
   ClientHello message was received.  This also decreases memory
   consumption if plain HTTP request is sent to SSL socket.