Use 'output' to configure EmPy v4 redirection (#666)

This aligns with our strategy for earlier EmPy versions and avoids an
assertion deep in EmPy v4 if 'output' is unspecified.

colcon_core/shell/template/__init__.py

@@ -43,9 +43,9 @@ def expand_template(template_path, destination_path, data):
  output=output, options={OVERRIDE_OPT: False})
  else:
  interpreter = CachingInterpreter(
+ output=output,
  config=Configuration(
  defaultRoot=str(template_path),
- defaultStdout=output,
  useProxy=False),
  dispatcher=False)
  try: