added a convenience method.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@9400 71c3de6d-444a-0410-be80-ed276b4c234a

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

@@ -250,6 +250,16 @@ public abstract class Computer extends AbstractModelObject {
         return new ArrayList<Executor>(executors);
     }
 
+    /**
+     * Returns true if all the executors of this computer is idle.
+     */
+    public boolean isIdle() {
+        for (Executor e : executors)
+            if(!e.isIdle())
+                return false;
+        return true;
+    }
+
     /**
      * Called by {@link Executor} to kill excessive executors from this computer.
      */