[yocto] care when using remove_packaging_data_files

[Chatre, Reinette]

Hi,

I am building an image using ipk packages. The minimal images all seem
to set ROOTFS_POSTPROCESS_COMMAND to remove_packaging_data_files, which
(for all package management systems) recursively removes the packages
directory in /var/lib. This seems a bit harsh considering that some
packages may still be in the unpacked state and thus have a script in
that directory that needs to be run when the image boots. 

ipk seems to cleanup without the need of remove_packaging_data_files -
rootfs_ipk.bbclass:rootfs_ipk_do_rootfs() checks if any packages are in
unpacked state and then will delete the packages directory in /var/lib
if nothing there is needed. I could not find similar actions in
rootfs_deb.bbclass or rootfs_rpm.bbclass 

I am thus planning on proceeding with my minimal image without setting
ROOTFS_POSTPROCESS_COMMAND, but it seems that minimal images based on
rpm and deb may need some changes to avoid surprises.

Reinette