Fied a couple of places where Task.getAssignedLabel() was invoked directly...

Fied a couple of places where Task.getAssignedLabel() was invoked directly without checking LabelAssignmentAction

core/src/main/java/hudson/model/Node.java

@@ -303,7 +303,7 @@ public abstract class Node extends AbstractModelObject implements Reconfigurable
      * @since 1.413
      */
     public CauseOfBlockage canTake(Queue.BuildableItem item) {
-        Label l = item.task.getAssignedLabel();
+        Label l = item.getAssignedLabel();
         if(l!=null && !l.contains(this))
             return CauseOfBlockage.fromMessage(Messages._Node_LabelMissing(getNodeName(),l));   // the task needs to be executed on label that this node doesn't have.
 

core/src/main/java/hudson/model/labels/LabelAssignmentAction.java

@@ -14,7 +14,10 @@ import hudson.model.queue.SubTask;
  */
 public interface LabelAssignmentAction extends Action {
     /**
+     * Reassigns where the task gets run.
      *
+     * @param task
+     *      Never null.
      * @return
      *      null to let other {@link LabelAssignmentAction}s take control, eventually to {@code SubTask#getAssignedLabel()}.
      *      If non-null value is returned, that label will be authoritative.

core/src/main/java/hudson/model/queue/MappingWorksheet.java

@@ -34,6 +34,7 @@ import hudson.model.Queue.BuildableItem;
 import hudson.model.Queue.Executable;
 import hudson.model.Queue.JobOffer;
 import hudson.model.Queue.Task;
+import hudson.model.labels.LabelAssignmentAction;
 
 import java.util.AbstractList;
 import java.util.ArrayList;
@@ -181,7 +182,7 @@ public class MappingWorksheet {
             super(base);
             assert !base.isEmpty();
             this.index = index;
-            this.assignedLabel = base.get(0).getAssignedLabel();
+            this.assignedLabel = getAssignedLabel(base.get(0));
 
             Node lbo = base.get(0).getLastBuiltOn();
             for (ExecutorChunk ec : executors) {
@@ -193,6 +194,14 @@ public class MappingWorksheet {
             lastBuiltOn = null;
         }
 
+        private Label getAssignedLabel(SubTask task) {
+            for (LabelAssignmentAction laa : item.getActions(LabelAssignmentAction.class)) {
+                Label l = laa.getAssignedLabel(task);
+                if (l!=null)    return l;
+            }
+            return task.getAssignedLabel();
+        }
+
         public List<ExecutorChunk> applicableExecutorChunks() {
             List<ExecutorChunk> r = new ArrayList<ExecutorChunk>(executors.size());
             for (ExecutorChunk e : executors) {