Restructured and updated basic environment config chapter

As part of the installation guide improvement project, I performed
the following operations on the basic environment configuration
chapter of the installation guide:

1) Split large ch_basics.xml file into smaller files to ease addition
   of new networking content and future updates.
2) Added information on how to install on VMs.
3) Added recommended minimum hardware requirements for each node.
4) Built detailed instructions for network configuration on
   three-node neutron and two-node nova example architectures
   including verification of connectivity using name resolution.
5) Clarified phrasing and wording.
6) Updated glossary as necessary.

This patch primarily updates networking content in this chapter.

Change-Id: Ib31a99448757d36ae29ff8069ddbeab8fe0106bd
Partial-Bug: #1291071
Implements: blueprint networking-install-guide-improvements