Classify `HealthTest-*` functions

[ndemou]

A nice classification of health test function in categories will be nice to have.

Is this classification of HealthTest-* functions good or should I tweak definition of classes or add/subtract some?

1. (Security) Attack Surface Reduction: detect deviations from widely accepted design rules, build standards and minimal hardening rules.
2. (Security) List security related system state to detect deviations from custom security/hardening rules.
3. (Functionality) Check if a component is failing or degraded (e.g. low or out of resources, failing to communicate, etc).
4. (Functionality) List non-security related system state to detect deviations from custom configurations.

Any other classifications we should have?