Add quad-9 server

test/pytest/test_dns.py

@@ -40,7 +40,7 @@ def test_dns(host):
         authorative_nameservers.append(ips[0].address)
 
     system_nameservers = dns.resolver.get_default_resolver()
-    external_nameservers = ['1.1.1.1', '8.8.8.8']
+    external_nameservers = ['1.1.1.1', '8.8.8.8', '9.9.9.9']
 
     results = []
     print('\nTesting authorative nameservers:')