mount of /.dockerinit is not needed for native driver, so move it into lxc driver

Docker-DCO-1.1-Signed-off-by: Albert Zhang <zhgwenming@gmail.com> (github: zhgwenming)
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)
systemd unitfile requires docker.socket

	modified:   contrib/init/systemd/docker.service

Docker-DCO-1.1-Signed-off-by: Lokesh Mandvekar <lsm5@fedoraproject.org> (github: lsm5)
since moved the ./dockerinit mount into lxc driver, fix the lxc testcase accordingly

Docker-DCO-1.1-Signed-off-by: Albert Zhang <zhgwenming@gmail.com> (github: zhgwenming)
Add "Acquire::GzipIndexes" to contrib/mkimage/debootstrap

This results in a dramatic improvement in the size of individual "apt-get update" layers (on a clean wheezy base, from "29.88 MB" down to "8.273 MB").

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
don't allow links to be used with --net=host

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
Merge pull request #7064 from tianon/debootstrap-gzipindexes

Add "Acquire::GzipIndexes" to contrib/mkimage/debootstrap
Merge pull request #6797 from zhgwenming/master

make /.dockerinit bind mount driver specific
Merge pull request #7066 from unclejack/disallow_links_with_nethost

don't allow links to be used with --net=host
Merge pull request #7021 from lsm5/systemd-maintainer

Add systemd MAINTAINERS file and update docker.service to always use socket activation