Project: mesos
Issue MESOS-3308: Define the container rootfs directories within the slave work_dir.
A few motivations: 1) Given the design in MESOS-3004 it became apparent that we need to support multiple images in a container and these images can be of different image types. (There are no sufficient reasons or major obstacles that force us not to allow it and it obviously gives the users more flexibility). 2) Also, even though we currently allow only one backend for each provisioner, when we update a running slave there can be multiple backends left in each container that we need to launch tasks with, or at least recover. We should evaluate in the future whether to support multiple backends and choose among them dynamically based on image characteristics. 3) Since the rootfs' lifecycle tie with the running containers and should be cleaned up after containers die, it fits into the pattern of {{word_dir}} and we can manage them inside the work dir without needing to ask the operator to specify more flags.
Story points: 2