Update the task pool demo to show re-use of recyclable jobs

Update the task pool demo to show re-use of recyclable jobs

The example now creates a recyclable job, schedules it and returns it
back to the task pool when it is done. It then again creates a
recyclable job and ensures that the task pool the same job present
it its cache.

git-svn-id: https://svn.code.sf.net/p/freertos/code/trunk@2687 1d2547de-c912-0410-9cb9-b8ca96c0e9e2