Increased number of retries and added variable delay to better withstand StorageException timeout.

Change-Id: Ic33d4e66e2787c717f7e3c90879d725a6e3e74d7
diff --git a/utils/misc/src/main/java/org/onlab/util/Tools.java b/utils/misc/src/main/java/org/onlab/util/Tools.java
index d9eb111..73c8802 100644
--- a/utils/misc/src/main/java/org/onlab/util/Tools.java
+++ b/utils/misc/src/main/java/org/onlab/util/Tools.java
@@ -39,6 +39,7 @@
 import java.util.Collection;
 import java.util.Dictionary;
 import java.util.List;
+import java.util.Random;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Future;
@@ -62,6 +63,8 @@
 
     private static final Logger log = getLogger(Tools.class);
 
+    private static Random random = new Random();
+
     /**
      * Returns a thread factory that produces threads named according to the
      * supplied name pattern.
@@ -195,6 +198,20 @@
     }
 
     /**
+     * Suspends the current thread for a random number of millis between 0 and
+     * the indicated limit.
+     *
+     * @param ms max number of millis
+     */
+    public static void randomDelay(int ms) {
+        try {
+            Thread.sleep(random.nextInt(ms));
+        } catch (InterruptedException e) {
+            throw new RuntimeException("Interrupted", e);
+        }
+    }
+
+    /**
      * Suspends the current thread for a specified number of millis and nanos.
      *
      * @param ms    number of millis