test: mark test-tty-wrap as flaky for AIX

We have had https://github.com/nodejs/node/issues/9728
open for a while but the frequency of the failures
seems to be such that we should mark it as flaky
while we continue to investigate.

PR-URL: https://github.com/nodejs/node/pull/10618


Reviewed-by: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>