HBASE-20509 putting List in HashSet directly without using addAll function to improve performance

Signed-off-by: Jan Hentschel <jan.hentschel@ultratendency.com>

Author: taiynlee

hbase-server/src/main/java/org/apache/hadoop/hbase/favored/FavoredNodeAssignmentHelper.java

@@ -395,8 +395,7 @@ private ServerName[] multiRackCaseWithRestrictions(
     rackSkipSet.add(primaryRack);
     String secondaryRack = getOneRandomRack(rackSkipSet);
     List<ServerName> serverList = getServersFromRack(secondaryRack);
-    Set<ServerName> serverSet = new HashSet<>();
-    serverSet.addAll(serverList);
+    Set<ServerName> serverSet = new HashSet<>(serverList);
     ServerName[] favoredNodes;
     if (serverList.size() >= 2) {
       // Randomly pick up two servers from this secondary rack
@@ -433,8 +432,7 @@ private ServerName[] multiRackCaseWithRestrictions(
         }
         secondaryRack = getOneRandomRack(rackSkipSet);
         serverList = getServersFromRack(secondaryRack);
-        serverSet = new HashSet<>();
-        serverSet.addAll(serverList);
+        serverSet = new HashSet<>(serverList);
       }
 
       // Place the secondary RS