Install Guide: Add auth_uri

Add auth_uri to [filter:authtoken]

Change-Id: If2d92169c4de3bf5414e9429f9d3a32d2ccad237
Partial-Bug: 1245911
Closes-Bug: 1245975
backport: havana
(cherry picked from commit 443556d1fadc02656b98f0f811c468c0c8460028)
Merge "Install Guide: Add auth_uri" into stable/havana