skip default values in dns record test

tests/test_dns_records.py

@@ -85,11 +85,19 @@ conf_servers = (
     'MONITOR_SERVER_NAME',
     'CM_SERVER_NAME',
 )
+
+conf_server_defaults = (
+    'mediaserver',
+    'monitor',
+    'campusmanager',
+)
+
 for s in conf_servers:
     hostname = conf.get(s)
-    ok = check_dns(hostname, ip)
-    if not ok:
-        all_ok = False
+    if hostname not in conf_server_defaults:
+        ok = check_dns(hostname, ip)
+        if not ok:
+            all_ok = False
 
 if not all_ok:
     sys.exit(1)