The goal here is to create a local mirror of the upstream OSTree repository.
Log into a shell on the host, and run the tools container. This isn't
strictly necessary right now as we could use the host's ostree
binary
too, but in the future the tools container might contain more scripts
for things like this. Once we're inside the tools container, we make
an unprivileged user, as general best practice. It also shows that
OSTree is perfectly happy to mirror/manipulate content as non-root.