tools: rinaperf: use a semaphore to properly manage free threads
tools: rinaperf: use a semaphore to properly manage free threads

This removes the need for 10 ms polling.

vmaffione/rlite,autrimpo/rlite,autrimpo/rlite,vmaffione/rlite,vmaffione/rlite,autrimpo/rlite,vmaffione/rlite,autrimpo/rlite