Add default rng device

Change-Id: I78c7975b1d949c4e7654a96bc42bc365f387420c
diff --git a/predefine-vm/define-vm.sh b/predefine-vm/define-vm.sh
index 7914c94..aed616a 100755
--- a/predefine-vm/define-vm.sh
+++ b/predefine-vm/define-vm.sh
@@ -87,6 +87,9 @@
     <graphics type='vnc' port='-1' autoport='yes' listen='127.0.0.1'>
       <listen type='address' address='127.0.0.1'/>
     </graphics>
+    <rng model='virtio'>
+      <backend model='random'>/dev/random</backend>
+    </rng>
   </devices>
 </domain>
 EOF