Keep only the latest artifacts for contrail build job

Change-Id: I204c584098afb2c7607378b06e1d230a5f434171
diff --git a/jenkins/client/job/opencontrail/build/generic.yml b/jenkins/client/job/opencontrail/build/generic.yml
index 1506326..0f130c4 100644
--- a/jenkins/client/job/opencontrail/build/generic.yml
+++ b/jenkins/client/job/opencontrail/build/generic.yml
@@ -140,7 +140,7 @@
              build:
                keep_num: 5
              artifact:
-               keep_num: 5
+               keep_num: 2
             type: workflow-scm
             concurrent: true
             quiet_period: 120