Many dependencies were pulled via dracut->systemd. Since we can build
stripped images without initrd and dracut, we need to add systemd
runtime dependencies explicitely.
User accounts of given names are necessary for the build script and
tests to succeed.
(Fixup of #15527, too keen cleaning of dependencies and cached image
caused this.)
The setup is meant to run against openSUSE Tumbleweed and install
minimum packages necessary for successful build and passing tests.
To speed up incremental build an external build directory is used.
Yu Watanabe