Brings up four projects:
- one to host the VPC
- two to use the VPC
- one which is outside the VPC
This is based on the diagram in https://cloud.google.com/vpc/docs/shared-vpc and uses the names there where possible for clarity.
On one of the machines, a page is generated demonstrating that the networking is working the way you'd expect. That machine's public IP is output by `terraform apply`.
- Fetch Zone attribute any place where it *was* being fetched from the schema by
combination schema / provider-level attribute.
- Allow region to be unspecified if zone is specified.
- Switch one example to using provider-level zone as an example.
- Make provider-level zone optional. (Individual resources will fail if they can't find a zone.)
- Add tests for getZone and getRegion.