When upgrading container images from Kolla-based to TCIB-based, the
config files can't be read if we don't apply the new chown values unless
we re-use the same UIDs/GIDs as we had with Kolla; which is what we'll
do for now until we figure out an easy way to update config permissions
during the upgrade/update stage.
This introduces a new script, that will be injected in the base layer:
./uid_gid_manage.sh qemu nova
It'll first create the qemu user/group, then nova user/group.
The format aims to be simple:
<username> <uid> <gid> <optional homedir> <optional list of extra groups>
It's also removing instances of usermod which aren't needed anymore;
since we create the user / groups only in the images where they are
needed; which wasn't the case for Kolla where all users/groups were
created in the base image.
Note: we create the user/group before installing packaging so if
packaging creates directories and sets permissions, it'll be with the
right UID/GID (unless packaging overrides UID/GID but rarely do it).
(cherry picked from commit