test: fix flaky parallel/test-http2-client-upload

In parallel/test-http2-client-upload, the `client.destroy()`
call could terminate the connection before all data was sent
over the wire successfully.

Using `client.shutdown()` removes the flakiness.

Also, listen on `req.on('finish')` rather than the file stream’s
`end` event, since we’re not interested in when the source stream
finishes, but rather when the HTTP/2 stream finishes.

PR-URL: #17361
Refs: #17356
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Kyle Farnung <kfarnung@microsoft.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>

test/parallel/test-http2-client-upload.js

@@ -38,7 +38,7 @@ fs.readFile(loc, common.mustCall((err, data) => {
     function maybeClose() {
       if (--remaining === 0) {
         server.close();
-        client.destroy();
+        client.shutdown();
       }
     }
 
@@ -47,7 +47,7 @@ fs.readFile(loc, common.mustCall((err, data) => {
     req.resume();
     req.on('end', common.mustCall(maybeClose));
     const str = fs.createReadStream(loc);
-    str.on('end', common.mustCall(maybeClose));
+    req.on('finish', common.mustCall(maybeClose));
     str.pipe(req);
   }));
 }));