Courier should fail early if it receives a response it can't process

[epixa]

Courier deals in json responses, but if it doesn't receive a json response, it doesn't fail right away. Instead, responses start going through the chain of response handlers and such, and eventually a non-json response will cause a JS error when you attempt to access the property timed_out on a non-object.

We do need to make sure we're not sending courier bogus responses, but courier can probably fail earlier with a more useful error message when it does happen.

[elasticmachine]

Pinging @elastic/kibana-app-arch

[lukasolson]

This has been resolved through the many refactorings that have happened recently.