refactor: modernize sample tests

[JustinBeckwith]

So there's a lot going on here.

1. Dumping sinon and proxyquire in one set of sample tests in favor of just running the sample code
2. Using chai for assert.match instead of .includes, as it shows both bits of text when a test fails
3. Moving the system tests for automl into the upper level system test directory.
4. Explicitly skipping the automl tests. They were previously never getting run because they were in a subdirectory. They need to be addressed in a follow up PR.
5. Using us-central as a default region in a few places
6. Swapping nodejs-repo-tools for execa