go-tour: add log.Fatal to HTTP handlers exercise
go-tour: add log.Fatal to HTTP handlers exercise

This helps people diagnose the ListenAndServe error.

TBR=campoy
R=golang-codereviews
CC=golang-codereviews
https://codereview.appspot.com/115170043

Go-zh/tour-old,Go-zh/tour-old,minux/go-tour-zh,minux/go-tour-zh