1100610 - Improved Upgrade and Install Docs, and Fixed Migration 0009 Error

This PR fixes [BZ 1100610](https://bugzilla.redhat.com/show_bug.cgi?id=1100610).

It updates the upgrade and installation docs related to migration 0009. It improves error messages to the users when they end up in this situation, and the migration cannot continue by referring them to the online docs. It also updates the tests associated with the migration code I modified with my new approach on unit test writing.

If you want to manually test this, you should run Migration 0009 with a 2.3.x consumer still bound to Qpid, and you will not be able to complete the upgrade without this patch.
After talking with jortel this is the correct way to do it. From jortel:  "the pulp-agent service is just a symlink created by the rpm.  if you are running a dev install, you wont have it.  but, rpm installs will."