stream_base: homogenize req_wrap_obj use

Always use `req_wrap_obj` to allow calling `req->Done()` in stream
implementations.

PR-URL: https://github.com/nodejs/node/pull/10184


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>