Add Live snapshots section to Ops Guide

Implements support for live snapshots, new nova feature, when QEMU 1.3 and Libvirt 1.0.0 are available
Edits grammar and style in surrounding sections
Needs further stylistic edits to listings and headings to match other guides

Change-Id: I07283f02d59877465faadfc74079fa9757dc4390
author: nermina miller
Closes-Bug: #1111093
Merge "Add Live snapshots section to Ops Guide"