Log user info in auth_token middleware

Add logging for user information (like user name, tenant_id, roles) in
the auth_token middleware. This would make tracking down issues much
easier.

Change-Id: Ife4ce29d2f8e1a338a025dda4afbd7b563f6b8c1
Implements: blueprint user-info-logging-in-auth-token-middleware
Merge "Log user info in auth_token middleware"