Update coding style after pycodestyle 2.1.0

In pycodestyle 2.1.0, E305 was introduced, which requires two blank
lines after top level declarations, too.

See https://github.com/PyCQA/pycodestyle/issues/400

See also #10689; thanks @stepshal for first mentioning this issue and
initial patches

devscripts/generate_aes_testdata.py

@@ -23,6 +23,7 @@ def openssl_encode(algo, key, iv):
     out, _ = prog.communicate(secret_msg)
     return out
 
+
 iv = key = [0x20, 0x15] + 14 * [0]
 
 r = openssl_encode('aes-128-cbc', key, iv)