build: add rule to clean addon tests build

Add a `test-addons-clean` to the Makefile
to clean up files generated during testing addons.

PR-URL: https://github.com/nodejs/node/pull/11519


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>