Add vpython support to Python recipe module.

recipe_engine/unittests/run_test.py

 #!/usr/bin/env python
 # Copyright 2014 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 import json
 import os
 import re
 import subprocess
 import unittest
@@ skipping 28 matching lines @@
     os.environ[requests_ssl.ENV_VAR_IGNORE] = '1'
     os.environ['RANDOM_MULTILINE_ENV'] = 'foo\nbar\nbaz\n'
     try:
       return (
           ['python', script_path] + eng_args + ['run', recipe] + proplist)
     finally:
       os.environ[requests_ssl.ENV_VAR_IGNORE] = prev_ignore
 
   def _test_recipe(self, recipe, properties=None):
     proc = subprocess.Popen(
-        self._run_cmd(recipe, properties), stdout=subprocess.PIPE)
-    proc.communicate()
-    self.assertEqual(0, proc.returncode, '%d != %d when testing %s' % (
-        0, proc.returncode, recipe))
+        self._run_cmd(recipe, properties),
+        stdout=subprocess.PIPE,
+        stderr=subprocess.STDOUT)
+    stdout = proc.communicate()
+    self.assertEqual(0, proc.returncode, '%d != %d when testing %s:\n%s' % (
+        0, proc.returncode, recipe, stdout))
 
   def test_examples(self):
     tests = [
       ['step:example'],
       ['path:example'],
       ['raw_io:example'],
       ['python:example'],
       ['json:example'],
       ['uuid:example'],
 
@@ skipping 193 matching lines @@
             u'foo',
             u'bar',
             u'baz',
           ],
         })
 
 
 if __name__ == '__main__':
   unittest.TestCase.maxDiff = None
   unittest.main()