test: use no-save and no-package-lock flags

Use these flags when running make coverage so that a package-lock.json
file is not generated and npm does not attempt to save the deps to a
non-existent package.json file.

PR-URL: https://github.com/nodejs/node/pull/15196
Refs: https://github.com/nodejs/node/pull/15190/files#r136932786


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>