Update name server blacklisting mechanism

[tgreenx]

Purpose

This PR proposes to rework the name server blacklisting mechanism to only happen on no response for non-EDNS SOA queries. This comes after discussions and deliberation from the work group.

Context

Fixes #1411

Changes

• Rework name server blacklisting mechanism
• Remove blacklisting of specific queries in Test Cases
• Add or update documentation

How to test this PR

Tests should pass.
Manual testing from #1411:

$ zonemaster-cli --show-testcase 120.89.185.in-addr.arpa --level debug --show-testcase --test nameserver10 --test zone11 --no-ipv6 | grep -Ev "EXTERNAL_QUERY|DEPENDENCY_VERSION|Unspecified"

Seconds Level    Testcase       Message
======= ======== ============== =======
   0.00 DEBUG    Nameserver10   TEST_CASE_START Nameserver10.
   2.69 DEBUG    Nameserver10   IPv6 is disabled, not sending "NS" query to ns3.afrinic.net/2001:500:14:6100:ad::1.
   3.18 WARNING  Nameserver10   Expected RCODE but received erroneous response to an EDNS version 1 query. Fetched from the nameservers with IP addresses 80.77.240.44
   3.18 DEBUG    Nameserver10   TEST_CASE_END Nameserver10.
   0.00 DEBUG    Zone11         TEST_CASE_START Zone11.
   0.06 DEBUG    Zone11         IPv6 is disabled, not sending "NS" query to ns3.afrinic.net/2001:500:14:6100:ad::1.
   0.18 NOTICE   Zone11         No SPF policy was found for 120.89.185.in-addr.arpa.
   0.18 DEBUG    Zone11         System:Zone11:TEST_CASE_END testcase=Zone11

[marc-vanderwal]

Looks pretty good. Just some minor comments.