net/http/cgi: disable TestCopyError to try to fix darwin/386 on builder
net/http/cgi: disable TestCopyError to try to fix darwin/386 on builder

Update issue 4958.

R=golang-dev
CC=golang-dev
https://codereview.appspot.com/7434047

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