unix: fix tests on NetBSD 8.0
unix: fix tests on NetBSD 8.0

Use /dev/ptyp* instead of /dev/ttyp* which don't seem to be available on
NetBSD 8.0+ anymore.

Change-Id: Idda6cc91b8cd26f5488852027b8d918f35a5e8fb
Reviewed-on: https://go-review.googlesource.com/80615
Run-TryBot: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

multiplay/golang-sys,multiplay/golang-sys,golang/sys,multiplay/golang-sys,multiplay/golang-sys,golang/sys,golang/sys