Allow using cargo in env setup

Reworked code from main pigweed repository to work in recipes.
https://pigweed.git.corp.google.com/pigweed/pigweed/+/master/pw_env_setup/py/pw_env_setup/cargo_setup/__init__.py

Bug: 67
Change-Id: Ifaf3dff5f9a8d9deefd4e41928d69d7bc3924b46
4 files changed
tree: c4d8799f3f5c7f45047c9b24aa4d52cc4dd7be69
  1. infra/
  2. recipe_modules/
  3. recipes/
  4. .gitignore
  5. .style.yapf
  6. recipes.py