Experimental DNS no longer returns A record for AAAA query - EUCA-7206

Behaviour updated as per RFC 4074:

   Suppose that an authoritative server has an A RR but has no AAAA RR
   for a host name.  Then, the server should return a response to a
   query for an AAAA RR of the name with the response code (RCODE) being
   0 (indicating no error) and with an empty answer section ...

EUCA-7206
Merge remote-tracking branch 'origin/dev/sjones/EUCA-7206' into maint/3.3/testing