Merge pull request #3701 from jglick/SlaveComputer.getRetentionStrategy

SlaveComputer.getRetentionStrategy mistake led to launches of unused agent JVMs

core/src/main/java/hudson/slaves/SlaveComputer.java

@@ -801,7 +801,7 @@ public class SlaveComputer extends Computer {
 
     public RetentionStrategy getRetentionStrategy() {
         Slave n = getNode();
-        return n==null ? RetentionStrategy.INSTANCE : n.getRetentionStrategy();
+        return n==null ? RetentionStrategy.NOOP : n.getRetentionStrategy();
     }
 
     /**