Add vendored version of github.com/guelfey/go.dbus

We need this to do systemd API calls.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Add systemd.SdBooted()

This is a conversion of sd_booted() from libsystemd to go and checks
if the system was booted with systemd.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
systemd: Add bindings for some systemd dbus calls

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
cgroups: Add systemd implementation of cgroups

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Remount /var/lib/docker as --private to fix scaling issue

If an admin mounts all file systems as -rshared (Default on RHEL and Fedora)
we see a scaling problem as the number of container increase.

Basically every new container needs to have it new mounts in /var/lib/docker
shared to all other containers, this ends up with us only able to scale to
around 100 containers, before the system slows down.

By simply bind mounting /var/lib/docker on its and then setting it private,
the scaling issue goes away.