Fixes #13198

The output of netsh is encoded with ANSI encoding. So doesn't match with UTF-8 strings.
Write output as UTF-8 using powershell.

Change-Id: I6c7e93c590ed407f24ae847601d71df9523e028c
Reviewed-on: https://go-review.googlesource.com/16756
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>