Add lxc-autostart

Add lxc-autostart

This introduces a new lxc-autostart binary (and associated manpage)
which will let you start/shutdown/kill/restart any container that's
marked as lxc.start.auto=1. It respects the lxc.start.delay value,
sorts by lxc.start.order and filters by lxc.group.

By default it'll affect all containers that DO NOT have lxc.group
set. If -g is specified, ONLY containers in those group will be
affected. To have a command applied to all containers, the -a
argument can be used.

A -L flag is also offered for distributions wishing to start the
containers themselves while still using LXC's calculated order and
wait delays. Instead of performing the action, it'll print the container
name and (if relevant for the action) the wait time.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>