Minor fixes to Sahara UI Installation Guide

 * removed item #7 - it is not needed and is misleading
 * rephrased clarification for AUTO_ASSIGNMENT_ENABLED
 * renamed 'Nova Network' to 'Nova-Network' - seems like the later is
   the only name which is used

Partial-Implements: blueprint update-docs-icehouse
Change-Id: Ibb177820da8d44e1f70a8fd7273dadd57e81ad1e
Merge "Minor fixes to Sahara UI Installation Guide"