test,tools: limit lint tolerance of gc global

Lint rules permitted the `gc` global in any test file. This change
limits it to just the files that need it.

PR-URL: https://github.com/nodejs/node/pull/6324


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