Added Neutron configuration for Nova in dedicated compute install

The installation instructions for provisioning a dedicated compute
node alongside OpenStack Networking was incomplete. It did not cover
how to configure Nova itself to communicate and make use of Neutron
networking.

Change-Id: I6e4772f5460ff84109db21c28e4edd2ff7e45d7f
backport: havana
Closes-Bug: 1260566
(cherry picked from commit e445d6d283b728ed2853660e4cdcd9108b32bd39)