Edit Identity Service chapter of Cloud Admin Guide

Moves authentication middleware info from the logging subsection to the authentication middleware section
Adds info on domains to the concepts section
Updates grammar and style in the affected sections

Change-Id: I96858e4b5ebadbcce8872b08992a00a9d638d1a4
author: nermina miller
backport: havana
Closes-Bug: #1239359
Added sysctl -p in step 1 to activate changes in /etc/sysctl.conf in ubuntu

Change-Id: I8cd980e9b7be7b7e5a462976ff37b960fcbf8fd0
backport: havana
Closes-bug: #1250678
Merge "Added sysctl -p in step 1 to activate changes in /etc/sysctl.conf in ubuntu"
Merge "Edit Identity Service chapter of Cloud Admin Guide"