Add vpython support to Python recipe module.

recipe_modules/python/example.resources/test.py

+# Copyright 2017 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 argparse
+import os
+import sys
+
+
+def main():
+  parser = argparse.ArgumentParser()
+  parser.add_argument('--verify-enum34', action='store_true')
+  parser.add_argument('--verify-six', action='store_true')
+  opts = parser.parse_args()
+
+  if opts.verify_enum34:
+    import enum
+    assert enum.version == (1, 1, 6)
+  if opts.verify_six:
+    import six
+    assert six.__version__ == '1.10.0'
+  return 0
+
+
+if __name__ == '__main__':
+  sys.exit(main())
+
+
+##
+# Inline VirtualEnv "vpython" spec.
+#
+# Pick a test package with no dependencies from "/bootstrap/venv.cfg" that
+# differs from the package in "test.vpython" file.
+#
+# This is used in "example.py" along with the "--verify-enum34" flag.
+##
+# [VPYTHON:BEGIN]
+#
+# wheel: <
+#   name: "infra/python/wheels/enum34-py2"
+#   version: "version:1.1.6"
+# >
+#
+# [VPYTHON:END]
+##