testing: don't start timing a Parallel test until it's actually starting Fixes issue 5285.
testing: don't start timing a Parallel test until it's actually starting
Fixes issue 5285.

R=golang-dev, dvyukov
CC=golang-dev
https://codereview.appspot.com/13045044

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