Extended serialize function to be able to handle more parallel steps in one serial

Change-Id: I078be4b82a18dc75fea27a5fbd9a775b95343660
diff --git a/src/com/mirantis/mk/Common.groovy b/src/com/mirantis/mk/Common.groovy
index e71a551..88fd5c7 100644
--- a/src/com/mirantis/mk/Common.groovy
+++ b/src/com/mirantis/mk/Common.groovy
@@ -212,8 +212,15 @@
 def serial(steps) {
     stepsArray = entries(steps)
     for (i=0; i < stepsArray.size; i++) {
-        s = stepsArray[i]
-        dummySteps = ["${s[0]}": s[1]]
+        def step = stepsArray[i]
+        dummySteps = [:]
+        if(step[1] instanceof Iterable){
+            for(j=0;j < step[1].size; i++){
+                dummySteps.put(step[0],step[1][j])
+            }
+        }else{
+            dummySteps.put(step[0], step[1])
+        }
         parallel dummySteps
     }
 }