runtime: add more tests for LockOSThread() Just test some additional paths through the scheduler.
runtime: add more tests for LockOSThread()
Just test some additional paths through the scheduler.

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/7331044

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