Sonar suggestion - use a secure random number generator

Change-Id: I28075845555bcbc384a49e07353b3192c413b8f7
diff --git a/providers/null/src/main/java/org/onosproject/provider/nil/TopologyMutationDriver.java b/providers/null/src/main/java/org/onosproject/provider/nil/TopologyMutationDriver.java
index 85823ba..e10e3db 100644
--- a/providers/null/src/main/java/org/onosproject/provider/nil/TopologyMutationDriver.java
+++ b/providers/null/src/main/java/org/onosproject/provider/nil/TopologyMutationDriver.java
@@ -29,6 +29,7 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.security.SecureRandom;
 import java.util.List;
 import java.util.Map;
 import java.util.Random;
@@ -53,7 +54,7 @@
     private static final int WAIT_DELAY = 2_000;
     private static final int MAX_DOWN_LINKS = 5;
 
-    private final Random random = new Random();
+    private final Random random = new SecureRandom();
 
     private volatile boolean stopped = true;