Modify keystone-paste.ini file on Kilo upgrade

This change will allow Keystone to modify the keystone-paste.ini file
instead of referencing the Base configuration in Kilo upgrade testing. The Base
configuration that pre-dates Kilo will contain XmlBodyMiddleware, which has been removed.

Documentation has been add in the Kilo Release Notes.

https://wiki.openstack.org/wiki/ReleaseNotes/Kilo#Upgrade_Notes_5

Change-Id: Ice45bdd3c1d5a2a8d7dcda05ac895d03a070aaf4
Closes-Bug: #1398833
Merge "Modify keystone-paste.ini file on Kilo upgrade"