Atomic ycsb command line printing

The concurrent log output from the concurrent connection setup can garble the output otherwise

src/site/ycsb/Client.java

@@ -528,11 +528,12 @@ public final class Client {
 
   private static Properties parseArguments(String[] args) {
     Properties props = new Properties();
-    System.err.print("Command line:");
+    StringBuilder builder = new StringBuilder();
+    builder.append("Command line:");
     for (String arg : args) {
-      System.err.print(" " + arg);
+      builder.append(" ").append(arg);
     }
-    System.err.println();
+    System.err.println(builder.toString());
 
     Properties fileprops = new Properties();
     int argindex = 0;