Use ParseDirent to get the directory entries instead of manually parsing
them. This fixes the test on dragonfly where type Dirent doesn't have a
Reclen member.
Manually tested on darwin, dragonfly and freebsd.
Change-Id: I234c6aff78243fec8bba8784c1d4948fbbb4d027
Reviewed-on: https://go-review.googlesource.com/c/sys/+/183226
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Benny Siegert <bsiegert@gmail.com>