root_metadata: address file_data review feedback from @jzila
root_metadata: address file_data review feedback from @jzila

Issue: #553

keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/kbfs,keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client