Limit the number of builds to keep with artifacts for omec jobs

Change-Id: If0120e73a65fb52942de3a36eb1fac8fbcca14a2
diff --git a/jjb/omec-ci.yaml b/jjb/omec-ci.yaml
index b08885f..acd4e6e 100644
--- a/jjb/omec-ci.yaml
+++ b/jjb/omec-ci.yaml
@@ -892,7 +892,7 @@
     properties:
       - cord-infra-properties:
           build-days-to-keep: '{build-days-to-keep}'
-          artifact-num-to-keep: '{artifact-num-to-keep}'
+          artifact-num-to-keep: 2
 
     wrappers:
       - lf-infra-wrappers: