Refactor how net/data/verify_certificate_chain_unittest/*

net/data/verify_certificate_chain_unittest/target-signed-by-512bit-rsa/generate-chains.py

 #!/usr/bin/python
 # Copyright (c) 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Certificate chain with 1 intermediate and a trusted root. The target
 certificate is signed using a weak RSA key (512-bit modulus), and so
 verification is expected to fail."""
 
+import sys
+sys.path += ['..']
+
 import common
 
 # Self-signed root certificate (used as trust anchor).
 root = common.create_self_signed_root_certificate('Root')
 
 # Intermediate with a very weak key size (512-bit RSA).
 intermediate = common.create_intermediate_certificate('Intermediate', root)
 intermediate.set_key(common.get_or_generate_rsa_key(
     512, common.create_key_path(intermediate.name)))
 
 # Target certificate.
 target = common.create_end_entity_certificate('Target', intermediate)
 
-chain = [target, intermediate]
-trusted = common.TrustAnchor(root, constrained=False)
-time = common.DEFAULT_TIME
-key_purpose = common.DEFAULT_KEY_PURPOSE
-verify_result = False
-errors = """----- Certificate i=0 (CN=Target) -----
-ERROR: RSA modulus too small
-  actual: 512
-  minimum: 1024
-ERROR: Unacceptable modulus length for RSA key
-ERROR: VerifySignedData failed
-
-"""
-
-common.write_test_file(__doc__, chain, trusted, time, key_purpose,
-                       verify_result, errors)
+chain = [target, intermediate, root]
+common.write_chain(__doc__, chain, 'chain.pem')