lxc-autostart: Add a new --ignore-auto/-A flag

lxc-autostart: Add a new --ignore-auto/-A flag

When passed, this flag will cause lxc-autostart to ignore the value of
lxc.start.auto.

This then allows things like: lxc-autostart -s -a -A

Which will select all containers regardless of groups (-a), regardless
of whether they are actually marked as auto-started (-A) and will shut
them down (-s).

Update our init scripts to use the new feature.

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