dns check should be made against a domain authoritative server

[arthru]

Dns checks are made using the local dns resolver or a configured one.

By using a non authoritative resolver, we have to wait for dns propagation to be made, that could be long depending to the configured TTL.

I propose to use the dns resolver to find the authoritative server and then to make dns request against that authoritative server.

With that change, dns checks would be instantaneous

[stale]

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