[QT-709] Validate scenario samples

[ryancragun]

A week or two ago we changed some scenario variants in an older Vault branch but failed to update samples to remove some variants that had been deleted.

Because the matrices on sample subsets are inclusive instead of exclusive, any subset that contained the non-existent variants ended up with an empty subset sample field. When we tried to take an observation from an empty field it would result in a singular sample of just the scenario name. In practice that meant we tried to run every variant combination instead of a single sample element in the pipeline.

This changes our behavior to disallow sample fields that are empty by default. We now specifically consider whether or not the scenario has a matrix when determining whether a sample field is a scenario with no variants or subsets have excluded all of them.

We add support for validating sample fields into both enos scenario validate and enos scenario sample observe commands.

By default enos scenario validate will now ensure that all sample and sample subset fields are valid. You can now disable either scenario or sample validation by using the --no-samples or --no-scenarios flag.

The validation command still expects a scenario filter as its default arg for filtering scenarios. If you wish to target sample validation to specific sample or sample subset you can use the new --sample-name, --include and --exclude flags.

• validate: add support for validating samples into sample command
• acceptance: add invalid scenario sample combination to validate suite
• acceptance: add invalid scenario sample combination to sample observe suite
• make: Don't run Go test in verbose mode by default
• acceptance: split stdout and stderr in the enos acceptance runner

Checklist

• The commit message includes an explanation of the changes
• Manual validation of the changes have been performed (if possible)
• New or modified code has requisite test coverage (if possible)
• I have performed a self-review of the changes
• I have made necessary changes and/or pull requests for documentation
• I have written useful comments in the code

[rebwill]

Neat idea! And a good call, as this (missing an update to the samples) could certainly happen again at some point.