Agent monitoring for docker container health state

[binsky08]

Problem
If a docker container is up and running, the "Docker status" check is green, even if the container persists in "unhealthy" state.

Describe the solution you'd like
Docker containers can have different states like starting, unhealthy, healthy. It would be cool if the container status check not only checks the running state, but also ensures that the state is healthy, if present. A dedicated docker check would also be fine.