package: Ensure we iterate all the pool objects
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.
(From OE-Core master rev:
89c8493d4d85044cd72af2756569d15e87cd5947)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
