* Vendor google.golang.org/api/cloudbilling/v1
* providers/google: Add cloudbilling client
* providers/google: google_project supports billing account
This change allows a Terraform user to set and update the billing
account associated with their project.
* providers/google: Testing project billing account
This change adds optional acceptance tests for project billing accounts.
GOOGLE_PROJECT_BILLING_ACCOUNT and GOOGLE_PROJECT_BILLING_ACCOUNT_2
must be set in the environment for the tests to run; otherwise, they
will be skipped.
Also includes a few code cleanups per review.
* providers/google: Improve project billing error message
Add support for creating, updating, and deleting projects, as well as
their enabled services and their IAM policies.
Various concessions were made for backwards compatibility, and will be
removed in 0.9 or 0.10.
