Setup devtmpfs and /dev for autodev bind mounts.

Setup devtmpfs and /dev for autodev bind mounts.

If autodev is not specifically set to 0 or 1, attempts to determine if
systemd is being utilized and forces autodev=1 to prevent host system
conflicts and collisions.

If autodev is enabled and the host /dev is mounted with devtmpfs
or /dev/.lxc is mounted with another file system...

Each container created by a privileged user gets a /dev directory
mapped off the host /dev here:

	/dev/.lxc/${name}.$( hash $lxcpath/$name )

Each container created by a non-privileged user gets a /dev/directory
mapped off the host /dev here:

	/dev/.lxc/user/${name}.$( hash $lxcpath/$name )

The /dev/.lxc/user is mode 1777 to allow unpriv access.

The /dev/.lxc/{containerdev} is bind mounted into the container /dev.

Fallback on failure is to mount tmpfs into the container /dev.

A symlink is created from $lxcpath/$name/rootfs.dev back to the /dev
relative directory to provid a code consistent reference for updating
container devs.

Signed-off-by: Michael H. Warfield <mhw@WittsEnd.com>
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>