siab gate test to use 'stable' instead of 'latest'

Change-Id: I588d21feac91dfb12ed761483d05ab20df05378b
diff --git a/jjb/siab.yaml b/jjb/siab.yaml
index df0b311..a3a32d6 100644
--- a/jjb/siab.yaml
+++ b/jjb/siab.yaml
@@ -140,7 +140,7 @@
 
       - string:
           name: version
-          default: 'latest'
+          default: 'stable'
           description: 'Latest | Stable'
 
       - string: