fixed a IndexAlreadyExistsException error on startup (race condition)

gateway/engine/es/src/main/java/io/apiman/gateway/engine/es/ESClientFactory.java

@@ -225,7 +225,13 @@ public static void createIndex(JestClient client, String indexName, String setti
         request.source(source);
         JestResult response = client.execute(new CreateIndex.Builder(indexName).settings(source).build());
         if (!response.isSucceeded()) {
-            throw new Exception("Failed to create index: '" + indexName + "' Reason: " + response.getErrorMessage()); //$NON-NLS-1$ //$NON-NLS-2$
+            // When running in e.g. Wildfly, the Gateway exists as two separate WARs - the API and the
+            // runtime Gateway itself.  They both create a registry and thus they both try to initialize
+            // the ES index if it doesn't exist.  A race condition could result in both WARs trying to
+            // create the index.  So a result of "IndexAlreadyExistsException" should be ignored.
+            if (!"IndexAlreadyExistsException".equals(response.getErrorMessage())) { //$NON-NLS-1$
+                throw new Exception("Failed to create index: '" + indexName + "' Reason: " + response.getErrorMessage()); //$NON-NLS-1$ //$NON-NLS-2$
+            }
         }
     }