Refactor how net/data/verify_certificate_chain_unittest/*

net/data/verify_certificate_chain_unittest/serverauth-rsa-ku-keyencipherment/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, a trusted root, and a target
 certificate for serverAuth that has only keyEncipherment."""
 
+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)
 
 # Target certificate.
 target = common.create_end_entity_certificate('Target', intermediate)
 target.set_key(common.get_or_generate_rsa_key(
     2048, common.create_key_path(target.name)))
 target.get_extensions().set_property('extendedKeyUsage', 'serverAuth')
 target.get_extensions().set_property('keyUsage', 'critical,keyEncipherment')
 
-
-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')