Added test_cluster_names param to customer-based test salt model pipeline template

Change-Id: Ie84e69729181775934849ac5c8fe4df2d45bf66e
diff --git a/jenkins/client/job/salt-models/tests.yml b/jenkins/client/job/salt-models/tests.yml
index 9e6b8ac..c68e3d9 100644
--- a/jenkins/client/job/salt-models/tests.yml
+++ b/jenkins/client/job/salt-models/tests.yml
@@ -110,6 +110,10 @@
                     - addedContains:
                         commentAddedCommentContains: '^(?s:Patch Set \d+:.*(test|recheck|reverify)\s*)$'
             param:
+              TEST_CLUSTER_NAMES:
+                type: string
+                description: "Comma separated list of cluster names, empty string means all valid clusters"
+                default: "{{test_cluster_names}}"
               SALT_OPTS:
                 type: string
                 default: "--force-color"