There is the possibility that if we don't iterate through the multiprocessing
pool objects we might not catch return codes and this could lead to hung/zombie
processes either temproarily or on a wider scale. Adding this certainly doesn't
hurt anything and is better practise so we might as well do it.
Its not 100% clear if this fixes some issues or not.
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
