Update ADMIN_TOKEN description in docs

Blurb taken from etc/keystone.conf.sample

partially fixes: bug #1283943

Change-Id: If7dac1dd902b52618f1af50a971fe1602426fdcf
V3 xml responses should use v3 namespace.

Currently, all v3 xml responses use v2 namespace, But v2 and v3
are incompatible. This change will fix it.

Change-Id: I5818bb0a268ae0e48263d5ea5795fdebeae9c388
Closes-Bug: #1195813
Merge "Update ADMIN_TOKEN description in docs"
Merge "V3 xml responses should use v3 namespace."