Support multiple resources in config.yaml, each with different expected_metrics

[SafariMonkey]

This pull request allows test writers to specify multiple resources like so:

resources:
  -
    resource:
      account_id: "5be71766-6c4c-47b8-869a-9dd1e5db3451"
      id: "b2989523-3bac-4f14-ba43-7ad7453eff0e"
    expected_metrics:
      - cpu-usage
      - memory-usage
  -
    resource:
      account_id: "5be71766-6c4c-47b8-869a-9dd1e5db3451"
      id: "14f06ece-9da7-468e-a7ca-e9554fdbda10"
    expected_metrics:
      - disk-usage

This is very useful in situations where there are multiple types of resource which might take different code paths or have separate mappings.

This still supports the old method of specifying resources and expected metrics:

resource:
  account_id: "5be71766-6c4c-47b8-869a-9dd1e5db3451"
  id: "b2989523-3bac-4f14-ba43-7ad7453eff0e"
expected_metrics:
  - cpu-usage
  - memory-usage