Terratest e2e test

[RothAndrew]

This is rough, but it works. I want to get it looked at and merged before it gets any bigger.

Primary changes

• Add a Terratest-based E2E test in the new directory /test. It consists of a reusable Terraform module that creates an EC2 instance and a small golang project that is separate from the golang project in the /cli directory. Run the test with aws-vault exec your-profile-here -- make test-e2e

Secondary changes

• (:warning: potentially breaking if there is any automation that depends on these make targets) Rename the test and test-close Makefile targets to vm-init and vm-destroy
• Add Makefile target help: Lists all targets
• Add Makefile target test-e2e: Run the new Terratest-based E2E test
• Add Makefile target e2e-ssh: For test development, lets you ssh into the EC2 instance that was running the E2E test for debugging

To-Do

There's a lot to do here still. The way I want this to be looked at is as an MVP that sets up the framework.

• New docs
• terraform_ssh_e2e_test.go is really big, but 95% of it will look identical for every E2E test we make, so we should extract all the boilerplate into a different file (maybe something like test_harness.go)
• I promised to make any E2E tests runnable locally as well with minimal setup. That's not done yet.
• Need to obviously add more E2E tests
• Need to either use directly or ensure everything that e2e.sh does the new E2E tests do
• Need to incorporate the tests into the automated CI pipeline by setting up the /test e2e chatops trigger (see pipeline #81)
• Need to generally just cleanup and refactor a bunch of it to be more performant. Right now it's clunky and slow and can definitely be improved.