Changes in the test page of user manager
Handle reverse-lookup zones for unbound

By default unbound returns nothing for private reverse lookups. Here is some information about that from https://www.unbound.net/documentation/unbound.conf.html
--------
       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.
--------
Just specifying 'nodefault' did not work. I found other threads where people used this in unbound.conf
--------
local-zone: "49.10.in-addr.arpa" typetransparent
--------
Note that it works 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.
Sorted the provider names alphabetically
Improve test in unbound_add_domain_overrides

Actually the test condition happened to work OK! But this change makes it easier to understand what is really intended.
Merge pull request #1340 from phil-davis/patch-5
Merge pull request #1338 from SilvioGiunge/change_system_usermanager_settings_test_page
Merge pull request #1339 from dembeck/master