Revert "Trying ONOS 2.5 based image in periodic tests"

This reverts commit ac21e15d4dbe74ddea3557fd30fe0deeafbcac38.

Reason for revert: onos-2.5 is voltha-onos master

Change-Id: Ic7b1959098f4e091f8fe4d741f3b43bb16de89b9
diff --git a/jjb/voltha-scale.yaml b/jjb/voltha-scale.yaml
index ca5fc69..5424195 100644
--- a/jjb/voltha-scale.yaml
+++ b/jjb/voltha-scale.yaml
@@ -105,7 +105,7 @@
           onosReplicas: 3
           atomixReplicas: 3
           extraHelmFlags: '--set authRetry=true,dhcpRetry=true --set global.rw_core.core_timeout=60s --set global.log_correlation.enabled=true -f /home/jenkins/voltha-scale/voltha-values.yaml '
-          onosImg: andreacampanella/voltha-onos:voltha-onos-2.5
+          onosImg: andreacampanella/voltha-onos:olt-group-pkt-req-mcast-fix
 
       # multi-stack jobs
       - 'voltha-scale-measurements':