Fix default Apache config cleanup on Debian

The configuration file /etc/apache2/conf-available/openstack-dashboard.conf
is not properly cleaned on Debian Operating System.

Change-Id: Idd495fe9ca0adc70eaad2f59a8b3aee212b2e8e5
Source: https://packages.debian.org/wheezy/all/openstack-dashboard-apache/filelist