[tripleo] py27 tests are being removed

Greetings, Just in case you didn't see or hear about it. TripleO is removing all the py27 tox tests [1]. See the bug for details why. We really need to get CentOS-8 jobs in place ASAP for ussuri and train, that will continue to be the upstream CI teams focus until it's done. Thank you [1] https://review.opendev.org/#/q/topic:1861803+(status:open+OR+status:merged)