We already have the validate method that returns an AccessInfo object.
For auth_token middleware it would be simpler if the client returned
simply the token data so it presented the same way as other sources of
token data.
It would also help with the keystoneauth transition in auth_token as we
could bypass the keystoneclient.AccessInfo objects.
Closes-Bug: #1475041
Change-Id: Ifbe7a7004937d910739c325cc04ae7264a4498e0
a4584c4ba7