Update label for salt-formula tests

Jenkins nodes labeled "old16.04" were deleted

Change-Id: If57a195688f1abeb65858cb5527bc57fbde18f40
diff --git a/test-salt-models-pipeline.groovy b/test-salt-models-pipeline.groovy
index 0b4a4d6..ef26ea5 100644
--- a/test-salt-models-pipeline.groovy
+++ b/test-salt-models-pipeline.groovy
@@ -86,7 +86,7 @@
   return true;
 }
 
-def nodeLabel = 'old16.04'
+def nodeLabel = 'docker'
 
 timeout(time: 12, unit: 'HOURS') {
   node(nodeLabel) {