Hijack the DELETE .watches index delete endpoint.

This change disables the DELETE .watches index endpoint.

Fixes: elastic/elasticsearch#439

Original commit: elastic/x-pack-elasticsearch@2e66cd55fa

rest-api-spec/test/hijack/10_basic.yaml

@@ -26,6 +26,11 @@
           type: "watch"
           id: "foo"
 
+  - do:
+      catch: /not supported/
+      indices.delete:
+          index: ".watches"
+
   - do:
       catch: /not supported/
       update:

src/main/java/org/elasticsearch/watcher/rest/action/RestHijackOperationAction.java

@@ -37,6 +37,7 @@ public class RestHijackOperationAction extends WatcherRestHandler {
             controller.registerHandler(RestRequest.Method.POST, WatchStore.INDEX + "/_bulk", unsupportedHandler);
             controller.registerHandler(RestRequest.Method.PUT, WatchStore.INDEX + "/watch/_bulk", unsupportedHandler);
             controller.registerHandler(RestRequest.Method.PUT, WatchStore.INDEX + "/_bulk", unsupportedHandler);
+            controller.registerHandler(RestRequest.Method.DELETE, WatchStore.INDEX, unsupportedHandler);
         }
     }