Improve performance of "Preheating DNS cache" phase when running against clusters with vnodes enabled

Author: Matt Jurik

cstar/job.py

@@ -156,7 +156,7 @@ def create_lookup_thread(ip):
             return threading.Thread(target=lambda: get_host_by_addr(ip))
 
         print("Preheating DNS cache")
-        threads = [create_lookup_thread(ip) for ip in ips]
+        threads = [create_lookup_thread(ip) for ip in set(ips)]
 
         for thread in threads:
             thread.start()