Modify contrail branches for generateDS pkg

Contrail package generateDS does not have 5.0 branch,
so new parameter was added to be able to mirror this
package.

Change-Id: I40cdd0013bbeaa4dd15ed4c62970751737411894
diff --git a/jenkins/client/job/opencontrail/git-mirrors/downstream.yml b/jenkins/client/job/opencontrail/git-mirrors/downstream.yml
index f92d1a7..306866b 100644
--- a/jenkins/client/job/opencontrail/git-mirrors/downstream.yml
+++ b/jenkins/client/job/opencontrail/git-mirrors/downstream.yml
@@ -16,7 +16,7 @@
             - name: contrail-third-party
               branches: ${_param:contrail_branches}
             - name: contrail-generateDS
-              branches: ${_param:contrail_branches}
+              branches: ${_param:contrail_branches_generateDS}
             - name: contrail-sandesh
               branches: ${_param:contrail_branches}
             - name: contrail-packages