Adding onos-2.3 system testing support for Jenkins Pipelines

Change-Id: Ic44c287dee562d24c3eda6f8a06e4d995430574a
diff --git a/jjb/OnosSystemTest/onos-test-freestyle.yaml b/jjb/OnosSystemTest/onos-test-freestyle.yaml
index 1d2cbc7..3f55041 100644
--- a/jjb/OnosSystemTest/onos-test-freestyle.yaml
+++ b/jjb/OnosSystemTest/onos-test-freestyle.yaml
@@ -17,6 +17,7 @@
       - '2.0'
       - '2.1'
       - '2.2'
+      - '2.3'
       - 'master'
       - 'manually'