[TEST] Waits for security template to be created in XPackRestIT

This commit applies the same fix merged in  elastic/elasticsearch#4179 for XDocsClientYamlTestSuiteIT. It adds a waitForSecurityTemplate() method in order to wait for the security-index-template to be created by the SecurityTemplateService.

Original commit: elastic/x-pack-elasticsearch@1476f30e2d

elasticsearch/src/test/java/org/elasticsearch/xpack/test/rest/XPackRestIT.java

@@ -5,7 +5,19 @@
  */
 package org.elasticsearch.xpack.test.rest;
 
+import org.apache.http.HttpStatus;
 import org.elasticsearch.test.rest.yaml.ClientYamlTestCandidate;
+import org.elasticsearch.test.rest.yaml.ClientYamlTestResponse;
+import org.elasticsearch.xpack.security.SecurityTemplateService;
+import org.junit.Before;
+
+import java.io.IOException;
+import java.util.Map;
+import java.util.concurrent.atomic.AtomicReference;
+
+import static java.util.Collections.emptyList;
+import static java.util.Collections.emptyMap;
+import static java.util.Collections.singletonMap;
 
 /** Runs rest tests against external cluster */
 public class XPackRestIT extends XPackRestTestCase {
@@ -14,4 +26,32 @@ public class XPackRestIT extends XPackRestTestCase {
         super(testCandidate);
     }
 
+    /**
+     * Waits for the Security template to be created by the {@link SecurityTemplateService}.
+     */
+    @Before
+    public void waitForSecurityTemplate() throws Exception {
+        String templateApi = "indices.exists_template";
+        Map<String, String> params = singletonMap("name", SecurityTemplateService.SECURITY_TEMPLATE_NAME);
+
+        AtomicReference<IOException> exceptionHolder = new AtomicReference<>();
+        awaitBusy(() -> {
+            try {
+                ClientYamlTestResponse response = getAdminExecutionContext().callApi(templateApi, params, emptyList(), emptyMap());
+                // We don't check the version of the template - it is the right one when testing documentation.
+                if (response.getStatusCode() == HttpStatus.SC_OK) {
+                    exceptionHolder.set(null);
+                    return true;
+                }
+            } catch (IOException e) {
+                exceptionHolder.set(e);
+            }
+            return false;
+        });
+
+        IOException exception = exceptionHolder.get();
+        if (exception != null) {
+            throw new IllegalStateException("Exception when waiting for security template to be created", exception);
+        }
+    }
 }