* Resolve CNAME when creating dns-01 challenge
It may be desirable to host the dns-01 challenge in a zone other than
the one where the challenge is presented. For example, when validating
a.example.com, the challenge may need to live on example.org.
This change resolves CNAMEs encountered when determining the FQDN of the
challenge, and replaces them with the alias.
This PR is based on the original work in #584.
Co-authored-by: Gurvinder Singh <gurvinder.singh@uninett.no>
* review: feature-flip.
* review: restore acmedns test.
