Support group of tasks (Pod) constructs and API in Mesos.

There is a common need among different frameworks, that wants to start a group of tasks that are either depend or co-located with each other.

Although a framework can schedule individual tasks within the same offer and slave id, it doesn't have a way to describe dependencies, failure policies (if one of the task failed), network setup, and group container information, etc.

Want to create a epic to start the discussion around the requirements folks need, and see where we can lead this.