REP-819 Keystone V3 Filter

The mess that is Keystone v3! Comment on _everything_ so we can get this fixed up. =)
Not entirely certain. This is another artifact pulled in from the Keystone v2 filter.

In the code, I just add this value to the admin token request as another qualifier. So I guess it's just  another constraint to make sure we get the correct token? Though if usernames are unique, that shouldn't make a difference. Another ask Jorge?