Fix XmlTestUtilsTest in open source build

The ExpectedException @Rule does not appear to be be able to catch
AssertionError in the version of JUnit we're tracking in the open source
world. This caused the expected exceptions to get passed through and
treated as failures.

The solution is to just use our forked version of ExpectedException,
which is ExceptionRule.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=128988393

javatests/google/registry/xml/BUILD

@@ -23,6 +23,7 @@ java_library(
         "//third_party/java/truth",
         "//java/google/registry/util",
         "//java/google/registry/xml",
+        "//javatests/google/registry/testing",
     ],
 )
 

javatests/google/registry/xml/XmlTestUtilsTest.java

@@ -17,9 +17,9 @@ package google.registry.xml;
 import static google.registry.util.ResourceUtils.readResourceUtf8;
 import static google.registry.xml.XmlTestUtils.assertXmlEquals;
 
+import google.registry.testing.ExceptionRule;
 import org.junit.Rule;
 import org.junit.Test;
-import org.junit.rules.ExpectedException;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
 
@@ -28,7 +28,7 @@ import org.junit.runners.JUnit4;
 public class XmlTestUtilsTest {
 
   @Rule
-  public final ExpectedException thrown = ExpectedException.none();
+  public final ExceptionRule thrown = new ExceptionRule();
 
   void runTest(String file1, String file2) throws Exception {
     String s1 = readResourceUtf8(getClass(), "testdata/" + file1);
@@ -46,12 +46,12 @@ public class XmlTestUtilsTest {
     thrown.expect(AssertionError.class);
     runTest("simple.xml", "twoextensions_feeThenLaunch.xml");
   }
-  
+
   @Test
   public void testMultipleElementsInDifferentNamespaces() throws Exception {
     runTest("twoextensions_feeThenLaunch.xml", "twoextensions_launchThenFee.xml");
   }
-  
+
   @Test
   public void testMultipleElementsInDifferentNamespaces_differentValues() throws Exception {
     thrown.expect(AssertionError.class);