streaming requests interact badly with `pipeline(..)`

Here's a minimal reproduction, tested with node 14 and 15.
```javascript
// test.js
const request = require('superagent');
const fs = require('fs');
const util = require('util');
const pipeline = util.promisify(require('stream').pipeline);

const main = async () => {
const stream = fs.createReadStream('test.js');
const req = request.put('http://httpstat.us/200');
console.log('here');
await pipeline(stream, req);
console.log('there');
};

main().catch(err => console.log('err', err)).then(() => console.log('done'));
```

The PUT appears (from some tcpdumping and watching logging with `DEBUG=*`) to complete successfully, but `there` and `done` are never printed -- execution of `main` appears to just cease and node exits normally, suggesting that something, somewhere, isn't calling a callback. Maybe

Replacing `await pipeline(stream, req)` with
```javascript
await new Promise((res, rej) => stream.pipe(req).on('end', res).on('error', rej));
```
seems to work, but it doesn't catch an error when the `/200` is changed to `/400` a few lines higher (probably `end` is emitted first?).

I think the issue is that, as a writable stream, `req` should be emitting `finish` and not `end`, which is for readable streams.
* https://nodejs.org/api/stream.html#stream_event_finish
* https://nodejs.org/api/stream.html#stream_event_end