Install Guide: One more Debian config fix
Install Guide: One more Debian config fix

I missed one place in patch https://review.openstack.org/#/c/55090/.

Change-Id: I7d48796f91d1c90f048dd036f40d1c60f1f4d58c
backport: havana

openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,kairoaraujo/openstack-manuals,openstack/openstack-manuals,saeki-masaki/openstack-manuals,openstack/openstack-manuals,kairoaraujo/openstack-manuals,Akasurde/openstack-manuals,gongysh2004/openstack-manual,Akasurde/openstack-manuals,gongysh2004/openstack-manual,potsmaster/openstack-manuals,saeki-masaki/openstack-manuals,potsmaster/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals