Comment 12 for bug 1241275

Solved.

It turns that in my case this error was caused by Neutron using a stale (cached locally) cacert.pem from the "/var/lib/neutron/keystone-signing/".

Flushing the content of that directory before reinstalling my OpenStack cluster (without re-installing the entire Operating System) solved my issue.

However I would argue that neutron should do a better job on reporting errors...