Client side period validation of certificates should not be
fatal, as local clock skews are not so uncommon. The validation
should be left to the running servers.
- Remove this validation from TryLoadCertFromDisk().
- Add a new function ValidateCertPeriod(), that can be used for this
purpose on demand.
- In phases/certs add a new function CheckCertificatePeriodValidity()
that will print warnings if a certificate does not pass period
validation, and caches certificates that were already checked.
- Use the function in a number of places where certificates
are loaded from disk.