python: Fix invalid varable/function references.

python: Fix invalid varable/function references.

This code referred to "rows" where it meant to refer to "fetched_rows".
The patch resolves flake8 error:

  F821 undefined name 'rows'

python/build/nroff.py used a function fatal() that was not defined,
which raised the same type of error.

Signed-off-by: Russell Bryant <russell@ovn.org>
Acked-by: Ben Pfaff <blp@ovn.org>