Prevent some troubles with dig +trace / dig +short and certbot --dry-run

[camlafit]

Hello

This plugin use actually certbot --dry-run to check whether certificate could be generate to each host. This solution is very long as we do a full let's encrypt test.
Dry-run is a test mode then at any moment Let's encrypt could be change theirs responses and could be no more accurate.

dig +trace used previously in some case stop to CNAME response and return any final IN A.
alternc-nginx-ssl use a workaround with dig +short but in this case it's sensible to any resolver cache.

We must improve this test to be faster and more accurate.