Add HealthManager::HealthRequest

Change-Id: I9dd76e026520a150be505a0266510927ae00fc6e
Add FlappingStatusResponse and CrashedStatusResponse

Change-Id: If921a43333d9283012776dda5cd76cfad890eb87
Add HealthResponse

Change-Id: I90c153d3c1db8dcfa6503295f7fe37b59adebb39