tools: backport tools/install.py for headers

Backport the tools/install.py changes from 628a3ab0 that were missed
when 6fb0b92f backported the corresponding changes to the Makefile to
build the headers only archive.

PR-URL: https://github.com/nodejs/node/pull/4149


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>
Reviewed-By: Rod Vagg <rod@vagg.org>