Disable blacklisting for queries by NAMESERVER15

[marc-vanderwal]

Purpose

Some DNS operate autoritative DNS servers in environments that drop queries performed by the NAMESERVER15 test case, i.e. version.bind/CH/TXT and version.server/CH/TXT.

In those setups, the name servers in question could be mistakenly deemed unresponsive, causing subsequent queries not to be attempted at all. This leads to false warnings in other test cases.

This commit disables the blacklisting of name servers that do not respond to our version probes, preventing false warnings from being emitted.

Context

Fixes #1281 (or at least, the situation leading to the creation of the issue).

Changes

Disable blacklisting of name servers not responding to version.{bind,server}/CH/TXT queries.

How to test this PR

Before:

$ zonemaster-cli festo.press --test basic --test nameserver/nameserver15 --test zone/zone09
Seconds Level     Message
======= ========= =======
   0.22 WARNING   No response on MX query from name servers "185.136.96.210;185.136.97.210;185.136.98.210;185.136.99.210".

After:

$ zonemaster-cli festo.press  --test basic --test nameserver/nameserver15 --test zone/zone09
Seconds Level     Message
======= ========= =======
Looks OK.

[tgreenx]

@marc-vanderwal The specification of Nameserver15 is currently being updated. See zonemaster/zonemaster#1199. I propose that we wait for the implementation update and include your proposed change then.

[marc-vanderwal]

It depends on whether we want to include this fix in the upcoming fix release. I think it could be nice if it were; if we can’t, I can wait.

[matsduf]

I think we should have a broader solution instead of just fixing NAMESERVER15. If this is seen as a work-around waiting for the broader solution, it could be fine.

[ghost]

I've done some quick tests and this looks good to me.