Update hack/dind to mount cgroups on "/cgroup" instead of "/sys/fs/cgroup" for better compatibility

Fixes #5122

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)

hack/dind

@@ -10,7 +10,7 @@
 # Usage: dind CMD [ARG...]
 
 # First, make sure that cgroups are mounted correctly.
-CGROUP=/sys/fs/cgroup
+CGROUP=/cgroup
 
 [ -d $CGROUP ] || 
 	mkdir $CGROUP