rpm-ostree: Fix support for major version updates
rpm-ostree: Use AppStream to check for new major versions
Use AppStream metadata to check if we should offer an upgrade to the new major distribution release.
rpm-ostree: Do not re-active the service after initial setup
We don't need to re-activate the rpm-ostree daemon after the first initialization. This will be less of an issue once we have support for registering ourselves as an update driver.
rpm-ostree: Update some comments