The CL 28951 added TestLookupPort_Minimal, which was failing
on Plan 9, because lookupPort was not case-insensitive.

Change-Id: Ic80dd29dad4ffd1c84c2590e3d5d0e588ab2e6c2
Reviewed-on: https://go-review.googlesource.com/29051
TryBot-Result: Gobot Gobot <gobot@golang.org>
Run-TryBot: David du Colombier <0intro@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>