Comment 14 for bug 1527925

Well, that seems alright. However, Glance log definitely seems to point out to connection failures regarding Keystone. So I would guess that there is some intermittent network failure. I know this doesn't help you much but such a case is not easily reproducible, and rightly so because that would mean Keystone wasn't working correctly. So I would suggest changing your installation environment, maybe a different server or network. I'm hoping that you won't have the same problem.