Fix /dev/console

The change in https://github.com/dotcloud/docker/commit/ae85dd54582e94d36b146ab1688844ed58cc8df3 broke /dev/console support:

```
docker run -ti fedora bash -c "echo foo > /dev/console"
bash: /dev/console: Input/output error
```

This is because the /dev/console mknod doesn't work, pts files have to be on a devpts filesystem.
This PR reverts the above and then cleans up the code so that we just use a regular file to bind mount over.