Update label for salt-formula tests

Jenkins nodes labeled "old16.04" were deleted

Change-Id: If57a195688f1abeb65858cb5527bc57fbde18f40
diff --git a/test-salt-model-node.groovy b/test-salt-model-node.groovy
index 9fded2e..a0d62b3 100644
--- a/test-salt-model-node.groovy
+++ b/test-salt-model-node.groovy
@@ -28,7 +28,7 @@
 def distribRevision = env.DISTRIB_REVISION ?: 'nightly'
 def checkouted = false
 
-def nodeLabel = 'old16.04'
+def nodeLabel = 'docker'
 
 throttle(['test-model']) {
   timeout(time: 1, unit: 'HOURS') {