Add workaround to fix support for installtree without repo
    
    Sources should always point to the repository, however, right now we are in
    middle of the migration process to Payloads sources so only base
    repositories are migrated and they are more or less only reflecting user data.
    To solve this for now we are adding back support for .treeinfo file and not
    just repodata. This should be removed when payload source migration will be
    finished.
    
    Resolves: rhbz#1854825