Project: mesos
Issue MESOS-4490: Get container status information in slave. 
As part of MESOS-4487 an interface will be introduce into the `Containerizer` to allow agents to retrieve container state information. The agent needs to use this interface to retrieve container state information during status updates from the executor. The container state information can be then use by the agent to expose various isolator specific configuration (for e.g., IP address allocated by network isolators, net_cls handles allocated by `cgroups/net_cls` isolator), that has been applied to the container, in the state.json endpoint.
Story points: 3