http: destroy socket on error

Needs further investigation, the test passed without `--use-uv`.

Fixes failing test:
  test/simple/test-http-dns-fail.js

lib/http2.js

@@ -1088,6 +1088,7 @@ ClientRequest.prototype.onSocket = function(socket) {
     // and we need to make sure we don't double-fire the error event.
     req._hadError = true;
     parser.finish();
+    socket.destroy();
   }
   socket.on('error', errorListener);