Fixes #5160: Make the packaging Apache 2.4 compliant

Ticket: http://www.rudder-project.org/redmine/issues/5160

To be merged in master
This will trigger set -e error catching. Let's reverse it like this:

```
[ ! -e /etc/apache2/sites-enabled/${i} ] || rm -f /etc/apache2/sites-enabled/${i}
```