Sonar suggestion - use a secure random number generator

Change-Id: I28075845555bcbc384a49e07353b3192c413b8f7
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 a8c8a8b..0989010 100644
--- a/utils/misc/src/main/java/org/onlab/util/Tools.java
+++ b/utils/misc/src/main/java/org/onlab/util/Tools.java
@@ -32,6 +32,7 @@
 import java.nio.file.SimpleFileVisitor;
 import java.nio.file.StandardCopyOption;
 import java.nio.file.attribute.BasicFileAttributes;
+import java.security.SecureRandom;
 import java.time.Instant;
 import java.time.OffsetDateTime;
 import java.time.ZoneId;
@@ -72,7 +73,7 @@
 
     private static final Logger log = getLogger(Tools.class);
 
-    private static Random random = new Random();
+    private static Random random = new SecureRandom();
 
     /**
      * Returns a thread factory that produces threads named according to the