c/r: use criu option instead of lxc-restore-net

c/r: use criu option instead of lxc-restore-net

As of criu 1.5, the --veth-pair argument supports an additional parameter that
is the bridge name to attach to. This enables us to get rid of the goofy
action-script hack that passed bridge names as environment variables.

This patch is on top of the systemd/lxcfs mount rework patch, as we probably
want to wait to use 1.5 options until it has been out for a while and is in
distros.

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Acked-by: Serge E. Hallyn <serge.hallyn@ubuntu.com>