atomic: create update/install ostree repo vars
    
    Use install_repo for during the creation of the ISO during the
    run of a compose. Use update_repo for the configuration of the
    remote in the %post of kickstart that runs during a ISO install.
    
    For example, when we create the ISO during a pungi run we need
    to pull the ostree commit from the repo that was just created.
    
    During the compose we need to pull from:
    
        https://kojipkgs.fedoraproject.org/compose/atomic/rawhide/
    
    But we need to configure the remote for users to point to:
    
        https://kojipkgs.fedoraproject.org/atomic/rawhide/
    
    Which is where the commits get synced to after the compose.
    
    Signed-off-by: Dusty Mabe <dusty@dustymabe.com>