Make cwd and NODE_PATH absolute in test runner
Make cwd and NODE_PATH absolute in test runner

This CL makes the custom node_modules_path absolute, because Node
requires it to be an absolute path, and does the same thing with the
custom `cwd` argument. Else if you pass a custom `cwd` you'll get errors
in the test suite as running `mocha --config ./foo/config.js` doesn't
work; Mocha also wants the path to be absolute.

Bug: none
Change-Id: Ib626075f4dd1c00fa2998d55fda8c212b8e853c0
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2718297
Commit-Queue: Jack Franklin <993fcadce4d04090da2fefd557a0995e7966c8d5@chromium.org>
Commit-Queue: Paul Lewis <8915f5d5c39a08c5a3e8a8d7314756e4580816f9@chromium.org>
Auto-Submit: Jack Franklin <993fcadce4d04090da2fefd557a0995e7966c8d5@chromium.org>
Reviewed-by: Paul Lewis <8915f5d5c39a08c5a3e8a8d7314756e4580816f9@chromium.org>

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