Change http status of AuthorizationException to 403

Closes elastic/elasticsearch#55

Original commit: elastic/x-pack-elasticsearch@23006f238b

src/main/java/org/elasticsearch/shield/authz/AuthorizationException.java

@@ -22,6 +22,6 @@ public class AuthorizationException extends org.elasticsearch.shield.SecurityExc
 
     @Override
     public RestStatus status() {
-        return RestStatus.UNAUTHORIZED;
+        return RestStatus.FORBIDDEN;
     }
 }