net/http: deflake test Update issue 5005.
net/http: deflake test
Update issue 5005.

R=golang-dev, fullung, bradfitz
CC=golang-dev
https://codereview.appspot.com/7651045

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