Refactor how net/data/verify_certificate_chain_unittest/*

net/data/verify_certificate_chain_unittest/intermediate-restricts-eku-ok/generate-chains.py

 #!/usr/bin/python
 # Copyright (c) 2017 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 intermediate
 restricts the EKU to serverAuth, and the target has serverAuth +
 clientAuth. Verification is expected to succeed as this is consistent with
 the requested key purpose."""
 
+import sys
+sys.path += ['..']
+
 import common
 
 # Self-signed root certificate (used as trust anchor).
 root = common.create_self_signed_root_certificate('Root')
 
 # Intermediate certificate.
 intermediate = common.create_intermediate_certificate('Intermediate', root)
 intermediate.get_extensions().set_property('extendedKeyUsage',
                                            'serverAuth')
 
 # Target certificate.
 target = common.create_end_entity_certificate('Target', intermediate)
 target.get_extensions().set_property('extendedKeyUsage',
                                      'serverAuth,clientAuth')
 
-chain = [target, intermediate]
-trusted = common.TrustAnchor(root, constrained=False)
-time = common.DEFAULT_TIME
-key_purpose = common.KEY_PURPOSE_SERVER_AUTH
-verify_result = True
-errors = None
-
-common.write_test_file(__doc__, chain, trusted, time, key_purpose,
-                       verify_result, errors)
+chain = [target, intermediate, root]
+common.write_chain(__doc__, chain, 'chain.pem')