testEnterCredential observed to fail due to offline mirror.

Since downloading tool metadata seems inessential for the test, leaving it disabled as is the default.
503 Service Unavailable for http://mirrors.jenkins-ci.org/updates/updates/hudson.tasks.Ant.AntInstaller.json?id=hudson.tasks.Ant.AntInstaller&version=1.557-SNAPSHOT%2520(private-03%252F24%252F2014%252014%253A15%2520GMT-jenkins)

test/src/test/java/hudson/tools/JDKInstallerTest.java

@@ -2,7 +2,6 @@ package hudson.tools;
 
 import com.gargoylesoftware.htmlunit.html.HtmlForm;
 import com.gargoylesoftware.htmlunit.html.HtmlPage;
-import hudson.model.DownloadService;
 import hudson.tools.JDKInstaller.DescriptorImpl;
 import org.jvnet.hudson.test.HudsonTestCase;
 import hudson.model.JDK;
@@ -31,13 +30,10 @@ import org.xml.sax.SAXException;
  * @author Kohsuke Kawaguchi
  */
 public class JDKInstallerTest extends HudsonTestCase {
-    boolean old;
 
     @Override
     protected void setUp() throws Exception {
         super.setUp();
-        old = DownloadService.neverUpdate;
-        DownloadService.neverUpdate = false;
 
         File f = new File(new File(System.getProperty("user.home")),".jenkins-ci.org");
         if (!f.exists()) {
@@ -61,12 +57,6 @@ public class JDKInstallerTest extends HudsonTestCase {
         }
     }
 
-    @Override
-    protected void tearDown() throws Exception {
-        DownloadService.neverUpdate = old;
-        super.tearDown();
-    }
-
     public void testEnterCredential() throws Exception {
         HtmlPage p = createWebClient().goTo("/descriptorByName/hudson.tools.JDKInstaller/enterCredential");
         HtmlForm form = p.getFormByName("postCredential");