Don't return several times the same zone.

lookup_plugins/re2oapi.py

@@ -474,7 +474,7 @@ class LookupModule(LookupBase):
                         netaddr.IPAddress(net.first).reverse_dns.split('.')[32 - net_class:])[:-1]
                     res.append(zone6_name)
                     display.vvv("Found reverse zone {}".format(zone6_name))
-        return res
+        return list(set(res))
 
     def _rawquery(self, api_client, endpoint):
         display.v("Make a raw query to endpoint {}".format(endpoint))