Correctly parse IP:Port nameserver pairs

Change-Id: If524b2d961088745b7e20a279626971c53db9d7c
diff --git a/designate_tempest_plugin/services/dns/query/query_client.py b/designate_tempest_plugin/services/dns/query/query_client.py
index c4df36a..65552c7 100644
--- a/designate_tempest_plugin/services/dns/query/query_client.py
+++ b/designate_tempest_plugin/services/dns/query/query_client.py
@@ -40,7 +40,7 @@
     """A client which queries a single nameserver"""
 
     def __init__(self, nameserver, query_timeout):
-        self.nameserver = Nameserver(nameserver)
+        self.nameserver = Nameserver.from_str(nameserver)
         self.query_timeout = query_timeout
 
     def query(self, name, rdatatype):