Use parameter for parallelism in salt-model test

Change-Id: Iaad295a07671ee56403add66c0de1ac6338b7bb9
diff --git a/test-salt-models-pipeline.groovy b/test-salt-models-pipeline.groovy
index 622b86a..1fafac9 100644
--- a/test-salt-models-pipeline.groovy
+++ b/test-salt-models-pipeline.groovy
@@ -63,7 +63,7 @@
     stage("test-nodes") {
       def nodes = sh script: "find ./nodes -type f -name 'cfg*.yml'", returnStdout: true
       def buildSteps = [:]
-      def partitions = common.partitionList(nodes.tokenize(), 3)
+      def partitions = common.partitionList(nodes.tokenize(), PARALLEL_NODE_GROUP_SIZE.toInteger())
       for (int i=0; i< partitions.size();i++) {
         def partition = partitions[i]
         buildSteps.put("partition-${i}", new HashMap<String,org.jenkinsci.plugins.workflow.cps.CpsClosure2>())