Add support for Users/Roles/Permssions

[blkmajik]

This pull request does a few things (all in part to enable the rest of the Auth service from gRPC)

• Updates the .proto files to version 3.4 from upstream
• Adds ability to override specific gRPC exceptions. (internal feature, not a user feature)
• Adds slightly better traceback happienss with Python 3
• Adds ability to use the rest of the Auth service from gRPC
  • Adds User CRUD operations
  • Adds Role CRUD operations
  • Adds Authentication enable/disable
• Modified tests to use a consistent function for getting etcd connection. This function now actually pays attention to the URL passed in from pifpaf.
• Modified tests to start etcd up on a different port so as to not conflict with the system etcd.
• Fix 2 flake8 .. code-block issues in the existing code.