Migrate terraform state to GCP

Created by: davejrt

Currently the following terraform deployments rely on local state, and developers running a terraform apply then checking in there code + a state file into the repo. In doing so we assume the risk that developers could corrupt a state file or forget to check it in.

The following terraform deployments should be migrated to use remote state in GCP:

• https://github.com/sourcegraph/infrastructure/tree/master/cloud
• https://github.com/sourcegraph/infrastructure/tree/master/dns
• https://github.com/sourcegraph/infrastructure/tree/master/site24x7

TODO

Determine naming scheme for each deployment