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.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
packagedata: Show error when trying to change PE/PV/PR from runtime/pkgdata

PN/PE/PV/PR should never change between do_package and the following do_package_write_*
tasks. If any do change you would see build failure due to the wrong WORKDIR being
used for example.

This patch ensures that if something is going wrong we see the error earlier and
with some better warning about what the real problem is.

[YOCTO #4102 partial]

This is a rewritten version of a patch from Martin Jansa <martin.jansa@gmail.com>

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>