test: load common.js in all tests

common.js contains code that detects leaked variables.

In preparation for an eslint rule that will enforce loading common.js in
test files, load it everywhere it can be loaded and use an
`eslint-disable` comment for files that intentionally leak.

PR-URL: https://github.com/nodejs/node/pull/3157


Reviewed-By: Rod Vagg <rod@vagg.org>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>