Bug/burgundy/legacy storeconfigs export

    Add transaction-uuid key to catalog if it doesn't exist
    
    Since old versions of puppet don't have a transaction-uuid
    in their catalog, and since we need to support imports of data
    that was exported from prior versions of puppetdb, the
    catalog transformation logic needs to tolerate the
    absence of this key.
    
    This commit simply adds the key (with a value of `nil`) if the
    key isn't already present.