Stop previous TaskStack worker

Each time we delete all threads, a new TaskStack thread is started.
We need stop the previous one to avoid over memory consumption.

Change-Id: I2c835c4f8c7d3c17bdf900f2f7ea5d63ca5a806c
Signed-off-by: Emmanuel Berthier <emmanuel.berthier@intel.com>
Merge "Stop previous TaskStack worker" into pac-4.4