test: remove s_client from test-tls-ci-reneg-attack

Rewrite test-tls-ci-reneg-attack to use tls.renegotiate() instead of
external (and potentially unpredictable/quirky/buggy) s_client.

Refs: https://github.com/nodejs/node/pull/25676#issuecomment-457307881

PR-URL: https://github.com/nodejs/node/pull/25700


Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>