Add a dependency to `docker/swarmkit` in preparation for adding
first-class Swarm-wide service management inside the Docker Engine as
described in our ROADMAP.md.
Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
Signed-off-by: Jana Radhakrishnan <mrjana@docker.com>
Signed-off-by: Victor Vieux <vieux@docker.com>
Signed-off-by: Madhu Venugopal <madhu@docker.com>
