Fix MarkDown in Docker Registry API docs

Docker-DCO-1.1-Signed-off-by: Gabor Nagy <mail@aigeruth.hu> (github: Aigeruth)
Update libcontainer dep to fb67bb80b4205bece36ff70
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@docker.com> (github: crosbymichael)
Update native driver for libcontainer changes
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@docker.com> (github: crosbymichael)
Merge pull request #7019 from crosbymichael/update-libcontainer-july2

Update libcontainer to version fb67bb80b4205bece36ff7096ee7
Merge pull request #6994 from Aigeruth/fix/docs/registry_api

Fix MarkDown in Docker Registry API docs
add systemd MAINTAINERS file

	new file:   contrib/init/systemd/MAINTAINERS

Docker-DCO-1.1-Signed-off-by: Lokesh Mandvekar <lsm5@fedoraproject.org> (github: lsm5)
use systemd socket-activation by default

	modified:   contrib/init/systemd/docker.service
	renamed:    contrib/init/systemd/socket-activation/docker.socket -> contrib/init/systemd/docker.socket
	deleted:    contrib/init/systemd/socket-activation/docker.service

Docker-DCO-1.1-Signed-off-by: Lokesh Mandvekar <lsm5@fedoraproject.org> (github: lsm5)