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>

python/build/nroff.py

@@ -13,6 +13,7 @@
 # limitations under the License.
 
 import re
+import sys
 
 from ovs.db import error
 
@@ -108,6 +109,12 @@ def pre_to_nroff(nodes, para, font):
     s += '\n.fi\n'
     return s
 
+
+def fatal(msg):
+    sys.stderr.write('%s\n' % msg)
+    sys.exit(1)
+
+
 def diagram_header_to_nroff(header_node):
     header_fields = []
     i = 0