`kola` now follows symlinks when archiving an external test's `data/`
dir. So the recursive `data` symlink we have here breaks it.
Let's just move the shared files in its own directory and update the
symlinks.
Follow the precedent set in https://github.com/coreos/rpm-ostree/pull/2106
and rename the directory, to more clearly move away from the
"uninstalled" test model. Prep for Rust-based tests.
Jonathan Lebon
Joseph Marrero
Colin Walters