Added fix for slow performance between Glance and vCenter

Added list item to Prerequisite and limitations section that
advises uses to upgrade to a fix to speed copy speed between
Glance and vCenter. Also fixed some spacing issues elsewhere
that did not conform to OpenStack doc conventions.

Change-Id: Ia413f9410f4d4118416d3b853c801e812885997c
Closes-Bug: #1279125
Merge "Added fix for slow performance between Glance and vCenter"