Run CHO with onos-1.15 by default

Change-Id: Ie4e11326443a01bed87a48b684e9899c0213121d
diff --git a/jjb/OnosSystemTest/onos-test-pipeline.yaml b/jjb/OnosSystemTest/onos-test-pipeline.yaml
index c4b73e6..60c8e99 100644
--- a/jjb/OnosSystemTest/onos-test-pipeline.yaml
+++ b/jjb/OnosSystemTest/onos-test-pipeline.yaml
@@ -385,7 +385,7 @@
       - text:
          name: ONOSbranch
          default: |
-                   master
+                   onos-1.15
          description: "Branch of the onos"
 
       - choice: