In order to have each individual error displayed in the dashboard, the
error status of the metrics should be stored.

The error store is added to the metrics, so each panel can display it's
own individual error state if needed.

Specifics:

- Add error states as constants
- Add mutations to capture loading and error states in each metric
- Capture each of the conditions that can create a given error
- Add specs for specific error cases
- Add new error cases to be tested under different server responses.
- Refactor to use the testAction util.