log changes of states of services on hosts in systems
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:
'18.104.22.168': http: <Error>'22.214.171.124': <Error><Error>null
All possible state forms and their matching log messages are documented in spec.js.