http: fix racy test with a simpler version
http: fix racy test with a simpler version

This was seen breaking the slow arm5 builder:
http://godashboard.appspot.com/log/ec54ee302a70c07093e8f5c47454b3eb48768b77e1d8cc7943d8951f8b6696be

The test was unnecessarily complex and didn't benefit from
using httptest.Server. That just got in the way.

R=rsc
CC=golang-dev
http://codereview.appspot.com/4439088

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang