cmd/go: add -race flag to 'go list'
cmd/go: add -race flag to 'go list'

Causes the package dependencies to include those for race detection.
Fixes issue 5653.

R=golang-dev, dave, bradfitz
CC=golang-dev
https://codereview.appspot.com/13236045

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