win,msi: mark INSTALLDIR property as secure

Allows INSTALLDIR to be passed to the server MSIExec process during
installation.

PR-URL: https://github.com/nodejs/node/pull/8795
Fixes: https://github.com/nodejs/node/issues/6057


Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>