http: fix stalled pipeline bug

http: fix stalled pipeline bug

This is a two-part fix:

- Fix pending data notification in `OutgoingMessage` to notify server
  about flushed data too
- Fix pause/resume behavior for the consumed socket. `resume` event is
  emitted on a next tick, and `socket._paused` can already be `true` at
  this time. Pause the socket again to avoid PAUSED error on parser.

Fix: https://github.com/nodejs/node/issues/3332
PR-URL: https://github.com/nodejs/node/pull/3342
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>