node: ensure that streams2 won't `.end()` stdin

Stdin is purely read-only stream. Although, `net.Socket` might be used
to create it if stdin is in fact a Pipe or TCP socket, the
`stream.Duplex` should not try to call `.end()` on it.

Fix: https://github.com/iojs/io.js/issues/1068
PR-URL: https://github.com/iojs/io.js/pull/1233


Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>