codereview.py: Fix crash on auth error handling.
codereview.py: Fix crash on auth error handling.

In recent Python versions .reason is a read-only property that simply gives you the msg value.

Fixes issue 4024

R=golang-dev, adg
CC=golang-dev
http://codereview.appspot.com/6545052

Committer: Shenghou Ma <b563c57947dc20eb81988e3e3c22786764c14ca8@gmail.com>

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