Install Guide: reorder Compute steps for AMQP

* remove duplicated instructions for Ubuntu
* group AMQP settings for all distributions in a same step
* move AMQP settings to a more sensible place in the compute
  controller installation section

Change-Id: I9efd4fe93f189ef4c631afb05f07d646eb57c7c4
backport: havana
Fixes the typo error in Image-Guide

Change-Id: Ifb70adf66aad96a7651b726be95693b9c4f76e54
Closes-Bug: #1251467
Merge "Install Guide: reorder Compute steps for AMQP"
Merge "Fixes the typo error in Image-Guide"