Always mount a /run tmpfs in the container

All modern distros set up /run to be a tmpfs, see for instance:
https://wiki.debian.org/ReleaseGoals/RunDirectory

Its a very useful place to store pid-files, sockets and other things
that only live at runtime and that should not be stored in the image.

This is also useful when running systemd inside a container, as it
will try to mount /run if not already mounted, which will fail for
non-privileged container.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Upstream-commit: 905795ece624675abe2ec2622b0bbafdb9d7f44c
Component: engine

components/engine/graph/graph.go

@@ -254,6 +254,7 @@ func SetupInitLayer(initLayer string) error {
 		"/dev/pts":         "dir",
 		"/dev/shm":         "dir",
 		"/proc":            "dir",
+		"/run":             "dir",
 		"/sys":             "dir",
 		"/.dockerinit":     "file",
 		"/.dockerenv":      "file",