Allow CNAME overrides for unbound

[sjorge]

We allow for CNAME to be used in the host override for unbound.

This closes #1614.

[fichtner]

looks good, thanks!

[sjorge]

Hey @fichtner although the CNAME are properly returned (yay) some local resolvers seem to have issues with them.

This is because unbound does not include the recursive A and/or AAAA records :(
There is an excellent thread here http://unbound.net/pipermail/unbound-users/2009-March/000507.html

Looks like it will probably never work with unbound without having an authoritative server behind it.
Again back to trusty dnsmasq, for now.

I'm conflicted about it, although technically this PR is technically correct and working it has some weird issues that will confuse users endlessly.

Although it pains to say this, perhaps we should back this out again.
There is not clean way to offer CNAME records via unbound without having the domain backed by bind or nsd.

[sjorge]

Example difference between dnsmasq with --cname=test.example.org,test.vlan10.example.org vs unbound with CNAME.

dnsmasq

$ dig +short test.example.org
test.vlan10.example.org.
127.0.0.2

ssh, ping, ... are all happy with this.

unbound

$ dig +short test.example.org
test.vlan10.example.org.

ssh, ping, ... not happy. Stuff like firefox are.

[sjorge]

@fichtner bump

[fichtner]

yeah, agreed, I'll back it out.

[sjorge]

Yeah I switched back to dnsmasq for now, nothing wrong with it but I was initially really impressed with unbound too.