allow to query NS on root or tld nameservers

[scuben]

My current usecase is to fetch the authoritative nameservers for a given domain starting from the root nameservers. Thus i query a root nameserver for the tld (e.g. .ch) with type NS. With the DnsGetRecord Handler that worked well (I guess partly because dns_get_records does not support to use a specific nameserver). After switching to Dig Handler my code was broken because of the +noall cli argument for dig. With this PR I added +authority (and +answer which is not necessary but declarative this way) to the cli arguments which then show the nameservers under the AUTHORITY section.

[freekmurze]

Thanks!