Domain for which certificate is asked for can have a CNAME, so we should check it.
If domain has a CNAME, create the challange TXT record in the alias domain.
This is useful in the scenario where a company like us is using some DNS provider
which is not supported dynamically. We can then create a CNAME for records like
_acme-challenge.example.com -> example.aws.hosted.com
So this will allow us getting cert for *.example.com with creating txt record in route53 for above exxample.
