With this enhancement, you can mark a resource as unhealthy using an API call in Orchestration (heat), so that it will be replaced on a subsequent stack update. For example, if a server in a `ResourceGroup` fails, rather than blacklisting (which would mean non-contiguous indices and any replacement getting a new name) the server can be marked unhealthy so that Heat will replace it with a new one with the same name and index in the group. The new `mark-unhealthy` command allows a resource to be put in the CHECK_FAILED state. Any stack updates subsequently performed will replace the unhealthy resource (as they do with all resources in an *_FAILED state).