Wrap ResponseException in AssertionError in ILM/CCR tests (elastic#48489)

When checking for the existence of a document in the ILM/CCR integration
tests, `assertDocumentExists` makes an HTTP request and checks the
response code. However, if the repsonse code is not successful, the call
will throw a `ResponseException`. `assertDocumentExists` is often called
inside an `assertBusy`, and wrapping the `ResponseException` in an
`AssertionError` will allow the `assertBusy` to retry.

In particular, this fixes an issue with `testCCRUnfollowDuringSnapshot`
where the index in question may still be closed when the document is
requested.

Author: gwbrown

x-pack/plugin/ilm/qa/multi-cluster/src/test/java/org/elasticsearch/xpack/ilm/CCRIndexLifecycleIT.java

@@ -7,9 +7,9 @@
 
 import org.apache.http.entity.ContentType;
 import org.apache.http.entity.StringEntity;
+import org.apache.http.util.EntityUtils;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
-import org.apache.lucene.util.LuceneTestCase;
 import org.elasticsearch.client.Request;
 import org.elasticsearch.client.Response;
 import org.elasticsearch.client.ResponseException;
@@ -109,7 +109,6 @@ public void testBasicCCRAndILMIntegration() throws Exception {
         }
     }
 
-    @LuceneTestCase.AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/48461")
     public void testCCRUnfollowDuringSnapshot() throws Exception {
         String indexName = "unfollow-test-index";
         if ("leader".equals(targetCluster)) {
@@ -750,10 +749,27 @@ private static Object getIndexSetting(RestClient client, String index, String se
         return settings.get(setting);
     }
 
-    private static void assertDocumentExists(RestClient client, String index, String id) throws IOException {
-        Request request = new Request("HEAD", "/" + index + "/_doc/" + id);
-        Response response = client.performRequest(request);
-        assertThat(response.getStatusLine().getStatusCode(), equalTo(200));
+    private void assertDocumentExists(RestClient client, String index, String id) throws IOException {
+        Request request = new Request("GET", "/" + index + "/_doc/" + id);
+        Response response;
+        try {
+            response = client.performRequest(request);
+            if (response.getStatusLine().getStatusCode() != 200) {
+                if (response.getEntity() != null) {
+                    logger.error(EntityUtils.toString(response.getEntity()));
+                } else {
+                    logger.error("response body was null");
+                }
+                fail("HTTP response code expected to be [200] but was [" + response.getStatusLine().getStatusCode() + "]");
+            }
+        } catch (ResponseException ex) {
+            if (ex.getResponse().getEntity() != null) {
+                logger.error(EntityUtils.toString(ex.getResponse().getEntity()), ex);
+            } else {
+                logger.error("response body was null");
+            }
+            fail("HTTP response code expected to be [200] but was [" + ex.getResponse().getStatusLine().getStatusCode() + "]");
+        }
     }
 
     private void createNewSingletonPolicy(String policyName, String phaseName, LifecycleAction action, TimeValue after) throws IOException {