node: allow preload modules with -i

This gives us the ability to preload when using the node repl. This can
be useful for doing things like creating aliases.

Fixes: https://github.com/nodejs/node/issues/4661
PR-URL: https://github.com/nodejs/node/pull/4696


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>