test: fix flaky test-http2-create-client-connect

The first group of tests makes one more connection and leave the server
alive for longer. Otherwise the test is just catching that the server
has closed the socket, depending on timing.

This does not quite make the test pass yet, however. There are some
quirks with how the http2 code handles errors which actually affect
1.0.2 as well.

PR-URL: https://github.com/nodejs/node/pull/16130


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Rod Vagg <rod@vagg.org>