labsdns: Allow returning arbitrary A records, not CNAMEs
CNAMEs are problematic since if the same DNS server is responsible
for the returned CNAME zone as well clients expect it to internally
resolve and return the A record too. This is too complex for us,
so we just fake return an A record directly. This has TTL implications,
but right now these are in /etc/hosts managed by puppet so it is
not making the situation worse.
Followup to I4c90b8002409f5de9bdc48bc878c27348122ce6c