fix race between kp_wait and workload task execution

Following sequence makes workload task hang on pause:
 1. fork in fork_workload
 2. parent returns and signal vm to start running
 3. vm sends SIGINT to workload task in kp_wait
 4. child start running and calls pause() in fork_workload
 5. now child misses the signal and will never be wake up by SIGINT

This patch forces vm to wait for workload task go into sleep state
before sending SIGINT signal.
fix typo in run_test.sh