Install Guide: Add missing Ubuntu instruction for Neutron install
Install Guide: Add missing Ubuntu instruction for Neutron install

The step was missing instructions for Ubuntu and Debian, add them.

Change-Id: I065323428c772a718ec45b312104c23db92a14d4
backport: havana
Closes-Bug: #1245750
Closes-Bug: #1241880

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