[tripleo] Nominate Cédric Jeanneret (Tengu) for tripleo-validations core

Hi TripleO devs, The new Validation Framework is a big step further for the tripleo-validations project. In many ways, it improves the way of detecting & reporting potential issues during a TripleO deployment. As the mastermind of this new framework, Cédric brought a new lease of life to the tripleo-validations project. That's why we would highly benefit from his addition to the core reviewer team. Assuming that there are no objections, we will add Cédric to the core team next week. Thanks, Cédric, for your excellent work! =Gaël