log changes of states of services on hosts in systems

damkaChangelog(log, oldSystemState, systemState)

damkaChangelog will log messages corresponding to the transition from oldSystemState to systemState. log is expected to be an object with .info(message) and .error(message) methods.

State objects are objects of any of the following forms:

{ '': { http: <Error> } }
{ '': <Error> }

All possible state forms and their matching log messages are documented in spec.js.