Fix cache_dir and beaker paths on deployment.ini_tmpl

Right now there are these on deployment.ini_tmpl:

```
cache_dir = %(here)s/data
beaker.cache.data_dir = %(here)s/data/cache
beaker.session.data_dir = %(here)s/data/sessions
```

This means that directories are created on `/etc/ckan/default/` which apart from creating permissions problems is a horrible place to put caching stuff.

This should be simplified to:

```
cache_dir = /tmp/%(ckan.site_id)s/
```

Beaker will create all necessary dirs under this one.