Add Yaml validy check for salt-models test

Change-Id: I48c5318cdf63651d7bad98b498889f65426b9cd6
diff --git a/test-salt-models-pipeline.groovy b/test-salt-models-pipeline.groovy
index c931e60..fcfba0c 100644
--- a/test-salt-models-pipeline.groovy
+++ b/test-salt-models-pipeline.groovy
@@ -136,6 +136,10 @@
       }
     }
 
+    stage("Check YAML") {
+       sh("git diff-tree --no-commit-id --diff-filter=d --name-only -r HEAD  | grep .yml | xargs -I {}  python -c \"import yaml; yaml.load(open('{}', 'r'))\" \\;")
+    }
+
     stage("test-nodes") {
       if(checkouted) {
         def modifiedClusters = null