Right now docker puts swarm's control socket into the docker root dir
(e.g. /var/lib/docker).
This can cause some nasty issues with path length being > 108
characters, especially in our CI environment.
Since we already have some other state going in the daemon's exec root
(libcontainerd and libnetwork), I think it makes sense to move the
control socket to this location, especially since there are other unix
sockets being created here by docker so it must always be at a path that
works.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
