Add initial enterprise dev-server test

[pglass]

Changes proposed in this PR:

This adds an enterprise test to TestBasic. Right now, it doesn't do anything special with partitions or namespaces.

I updated things to pass a list of ECS clusters from setup-terraform through to test cases and (usually) through to Terraform. This fixes an issue I caused where the ECS cluster wasn't being passed correctly in HCP tests, and I fixed an issue with parallel terraform inits in TestBasic

How I've tested this PR:

• Acceptance tests in CI, and locally

How I expect reviewers to test this PR:

👀

Checklist:

• [x] Tests added
• [ ] CHANGELOG entry added