test: fix pummel test failures

A handful of tests in `test/pummel` were failing due to undefined
variables.

The tests in pummel are not run in CI or otherwise exercised regularly
so these failures can go unnoticed for a long time.

PR-URL: https://github.com/nodejs/node/pull/6012


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>