BUG/MEDIUM: connection: Don't use the provided conn_stream if it was tried.

BUG/MEDIUM: connection: Don't use the provided conn_stream if it was tried.

In connect_server(), don't attempt to reuse the conn_stream associated to
the stream_interface, if we already attempted a connection with it.
Using that conn_stream is only there for the cases where a connection and
a conn_stream was created ahead, mostly by http_proxy or by the LUA code.
If we already attempted to connect, that means we fail, and so we should
create a new connection.

No backport needed.