server selection: practical issues with some Microsoft domains

With some Microsoft domains (outlook.com, office.com, office365.com) a small part of the nameservers is non-responsive, but kresd (sometimes) does not gracefully fall back to the other servers.

The same issue can surely happen with someone else's names as well, but this set seems far the most commonly encountered in practice. It might be related to the NS server names being served by the same partially broken set.