nixos: add option for bind to not resolve local queries (#29503)

When the user specifies the networking.nameservers setting in the
configuration file, it must take precedence over automatically
derived settings.

The culprit was services.bind that made the resolver set to
127.0.0.1 and ignore the nameserver setting.

This patch adds a flag to services.bind to override the nameserver
to localhost. It defaults to true. Setting this to false prevents the
service.bind and dnsmasq.resolveLocalQueries settings from
overriding the users' settings.

Also, when the user specifies a domain to search, it must be set in
the resolver configuration, even if the user does not specify any
nameservers.

(cherry picked from commit 670b4e29adc16e0a29aa5b4c126703dcca56aeb6)

This commit was accidentally merged to 17.09 but was intended for
master. This is the cherry-pick to master.

nixos/modules/config/networking.nix

···
   cfg = config.networking;
   dnsmasqResolve = config.services.dnsmasq.enable &&
                    config.services.dnsmasq.resolveLocalQueries;
-  hasLocalResolver = config.services.bind.enable || dnsmasqResolve;
+  bindResolve =    config.services.bind.enable &&
+                   config.services.bind.resolveLocalQueries;
+  hasLocalResolver = bindResolve || dnsmasqResolve;
 
   resolvconfOptions = cfg.resolvconfOptions
     ++ optional cfg.dnsSingleRequest "single-request"

nixos/modules/services/networking/bind.nix

···
         ";
       };
 
+      resolveLocalQueries = mkOption {
+        type = types.bool;
+        default = true;
+        description = ''
+          Whether bind should resolve local queries (i.e. add 127.0.0.1 to
+          /etc/resolv.conf, overriding networking.nameserver).
+        '';
+      };
+
     };
 
   };

nixos/modules/services/networking/dnsmasq.nix

···
         default = true;
         description = ''
           Whether dnsmasq should resolve local queries (i.e. add 127.0.0.1 to
-          /etc/resolv.conf).
+          /etc/resolv.conf overriding networking.nameservers).
         '';
       };
 

nixos/modules/tasks/network-interfaces-scripted.nix

···
               ''
                 # Set the static DNS configuration, if given.
                 ${pkgs.openresolv}/sbin/resolvconf -m 1 -a static <<EOF
-                ${optionalString (cfg.nameservers != [] && cfg.domain != null) ''
+                ${optionalString (cfg.domain != null) ''
                   domain ${cfg.domain}
                 ''}
                 ${optionalString (cfg.search != []) ("search " + concatStringsSep " " cfg.search)}