test: fix flaky test-tls-wrap-timeout

Competing timers were causing a race condition and thus the test was
flaky. Instead, we check an object property on process exit.

Fixes: https://github.com/nodejs/node/issues/7650
PR-URL: https://github.com/nodejs/node/pull/7857


Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>
Reviewed-By: jasnell - James M Snell <jasnell@gmail.com>