net/http: fix test breakage on Windows
net/http: fix test breakage on Windows

Treat the Windows net server as uninteresting for leak
purposes too.

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/7818048

tv42/old-go,dsriram/golang,tv42/old-go,pombredanne/go-deleteme,gnanderson/go,gnanderson/go,apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme,gnanderson/go,pombredanne/go-deleteme,gnanderson/go,pombredanne/go-deleteme,tv42/old-go,dsriram/golang,apparentlymart/golang,dsriram/golang,gnanderson/go,apparentlymart/golang,dsriram/golang,apparentlymart/golang,dsriram/golang,pombredanne/go-deleteme,dsriram/golang,tv42/old-go,pombredanne/go-deleteme,dsriram/golang,apparentlymart/golang,tv42/old-go,apparentlymart/golang,gnanderson/go,gnanderson/go,pombredanne/go-deleteme,tv42/old-go,tv42/old-go