I think this was documented pretty well pre-redux (on a page called Concepts, as I recall), however I don't see any remnants of that documentation?
Regarding the error message, I think this is a bug against novaclient, as it appears that nova is perhaps suppressing/ignoring a more useful error message from keystone? (given the "Invalid tenant" warning in the OP's log)
I think this was documented pretty well pre-redux (on a page called Concepts, as I recall), however I don't see any remnants of that documentation?
Regarding the error message, I think this is a bug against novaclient, as it appears that nova is perhaps suppressing/ ignoring a more useful error message from keystone? (given the "Invalid tenant" warning in the OP's log)