Align API Health Response and Checks objects

[smoyer64]

As we've adopted the micro-service mind-set, we find ourselves with a larger and larger hierarchy of service calls being made from "aggregator" top-level services. For instance, since we use OAuth2 for authentication and Fortress (ANSI RBAC) for authorization, every one of these services will depend on those two. It's pretty easy to quickly have 4-5 micro-services in the hierarchy and in extreme cases these calls "fan-out" to 15 or 20 other systems.

I'd like to propose that the Checks object be aligned with the (top-level) API Health Check object and that an additional value of healthcheck be added to the pre-defined ComponentTypes listed in the specification. I'm a bit conflicted about whether another pre-defined MeasurementName (such as health) would be beneficial or if the MeasurementName should just be left off.

I do realize that it's still up to the service to determine how the healthcheck status of a subsystem affects its top-level status - some out-right failures of a subsystem will cause a degradation while others are more catastrophic - but I think there's a huge advantage in knowing that the format of the incoming data is another healthcheck.