We don't want to allow MITM attackers to intercept upgrade requests
and provide clients with older OS versions vulnerable to security
flaws.
Only "ostree admin upgrade" gets this behavior for now - whether we
want to do it for "ostree admin switch" is another question.
OSTree is a tool for managing bootable, immutable, versioned
filesystem trees. While it takes over some of the roles of tradtional
"package managers" like dpkg and rpm, it is not a package system; nor
is it a tool for managing full disk images. Instead, it sits between
those levels, offering a blend of the advantages (and disadvantages)
of both.