c/r: drop lxc.console=none config requirement

c/r: drop lxc.console=none config requirement

There are a few things going on in this patch.

1. /dev/console is an external mount since it is bind mounted from the
   host. However, we don't want to use criu's --ext-mount-map auto handling
   here, because that will bind mount exactly the same path from the host
   on restore, but if the pts device is different on the target host, we'll
   bind mount the wrong one, which is obviously wrong.

2. We need to tell CRIU how to restore the TTY. Since we declare the tty as
   --external, we need to provide it via --inherit-fd (even though we've
   already fixed up the environment).

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>