Update the docs for `google_project` with @zachgersh's suggestions
(#11895) to properly communicate the changes that took place in 0.8.5.
While they don't break any current configs or state, the new behaviour
should be called out for people who were using the old behaviour and are
adding new projects to their configs/state.
I also took this opportunity to update google_project_iam_policy with a
note to users letting them know that there be dragons.
* 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.
