Fix pigweed recipe.

Mostly fixing pigweed.py and creating two modules:
* checkout: retrieving code
* environment: cipd and virtualenv setup and use

The job currently fails, but this is a significant step towards getting
it to pass.

Change-Id: I8ff7ed50bcf8700917ea04eb116182590661f541
Bug: 3
12 files changed
tree: c84b5c563175a19c83e90d8816263ed6a584c0a7
  1. infra/
  2. recipe_modules/
  3. recipes/
  4. .gitignore
  5. recipes.py