Vault testing is failed if we want to
increase vault's default ttl to 10 years
because zaza specify cert's ttl is only 80days.
https://review.opendev.org/#/c/678161
The current usage of ``datetime.today()`` is at the grace of the
locale settings of the test executor and the instances spun up.
The ``cryptography.x509.CertificateBuilder`` ``not_valud_before``
and ``not_valid_after`` attributes do expect [0] a UTC datetime.
0: https://cryptography.io/en/latest/x509/reference/#cryptography.x509.CertificateBuilder