Handle reverse-lookup zones for unbound - fixes #4014

By default unbound returns nothing for private reverse lookups. Here is some information about that from https://www.unbound.net/documentation/unbound.conf.html
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       The  default  zones  are  localhost, reverse 127.0.0.1 and ::1, and the
       AS112 zones. The AS112 zones are reverse DNS zones for private use  and
       reserved IP addresses for which the servers on the internet cannot pro-
       vide correct answers. They are configured by default to  give  nxdomain
       (no  reverse  information)  answers.  The defaults can be turned off by
       specifying your own local-zone of that name, or using  the  'nodefault'
       type. Below is a list of the default zone contents.
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Just specifying 'nodefault' did not work. I found other threads where people used this in unbound.conf
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local-zone: "49.10.in-addr.arpa" typetransparent
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Note that it works if specifying the domain override with or without a final "." So the code here checks for the special cases of ".in-addr.arpa" and ".in-addr.arpa." at the end of a domain override name.

With this code my domain override entries for private reverse lookups work. I can traceroute around my internal network and the traceroute can show me the names that go with the private IP addresses at each hop.
Indeed - I had just search-replaced the var name and did not look at the existing test! I got lucky and actually the existing test happens to work. But yes, it would look much nicer if it was as you suggest. Will submit another commit...