Updates single flat use-case example for RHEL/CentOS/Fedora

Adds specific configuration options for RHEL, CentOS and Fedora
based distributions which were missing - e.g. the guide presumed
RabbitMQ was in use despite it not being relevant for these
platforms. In addition it adds clarity on where to find further
information or how to complete a specific step where necessary,
something the existing implementation lacked.

Now uses openstack-config in RHEL and SUSE based platforms.

Change-Id: I6c9a45114afbfa99ea2d01a3f682a0dc78a72530
backport: havana
Closes-Bug: 1266418
Merge "Updates single flat use-case example for RHEL/CentOS/Fedora"