api: some api client library methods mask the underlying error when non-200 status codes are received

[dnephin]

See #8816

Overview of the Issue

Copied from #8816

Consul agent returns errors in plain text. Yet when this happens the api client still tries to decode them in JSON, failing, and hiding the real error message.

It seems like some methods in the api client library do properly check the error code with requireOk, where as others do not. The methods that do not properly check the error code will error with JSON decode errors when the HTTP response was not 200. This error masks the real underlying problem, making the api client library difficult to use.

[acpana]

We merged #11054 to allow the error status code to be queried programmatically.

Keeping this issue open until I take a pass over all doRequest() func calls and make sure they're wrapped in requireHttpCodes() or return a StatusError type

[acpana]

@dnephin with PR #11158 I think we can close this issue. What do you think?

For the refactor discussed here #11158 (comment) I can open an issue to track visibility.

[dnephin]

Sounds good!