Disable all the scale jobs but the 2.4 ones

Change-Id: I2cb6a8a70d84b06b55a3e912b03b00ea61085d83
diff --git a/jjb/defaults.yaml b/jjb/defaults.yaml
index a3cee32..9243dae 100644
--- a/jjb/defaults.yaml
+++ b/jjb/defaults.yaml
@@ -4,6 +4,10 @@
 - defaults:
     name: global
 
+    # used to enable disable jobs if the job template contains
+    # disabled: '{disable-job}'
+    disable-job: false
+
     # lftools
     lftools-version: '~=0.26.2'