runtime: re-enable TestParForParallel
runtime: re-enable TestParForParallel

See how it flies. We'll disable it again if the underlying issue is not resolved.
See issue 4155 for details.

Fixes issue 4155.

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/13368045

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