[JENKINS-20662] Simplify test after feedback

test/src/test/groovy/jenkins/model/lazy/LazyBuildMixIn_Test.groovy

@@ -6,6 +6,7 @@ import hudson.model.listeners.RunListener
 import org.junit.Rule
 import org.junit.Test
 import org.jvnet.hudson.test.Bug
+import org.jvnet.hudson.test.SleepBuilder
 import org.jvnet.hudson.test.JenkinsRule
 
 class LazyBuildMixIn_Test {
@@ -15,16 +16,8 @@ class LazyBuildMixIn_Test {
     @Test
     @Bug(20662)
     public void testNewRunningBuildRelationFromPrevious() {
-        RunListener<Run> listener = new RunListener<Run>() {
-            @Override public  void onCompleted(Run r, TaskListener listener) {
-                try {
-                    Thread.sleep(1000);
-                } catch (InterruptedException e) {
-                }
-            }
-        };
-        RunListener.all().add(listener);
         def p = r.createFreeStyleProject();
+        p.buildersList.replaceBy([new SleepBuilder(1000)])
         def b1 = p.scheduleBuild2(0).get();
         assert null == b1.getNextBuild();
         def b2 = p.scheduleBuild2(0).waitForStart();