Added module result to output as attribute for better integration with Symfony

A minor change to provide better integration of legacy requests with the Symfony stack.

Full writeup here: 
https://github.com/ezsystems/ezpublish-kernel/pull/264

See also  
https://jira.ez.no/browse/EZP-20576
http://share.ez.no/forums/ez-publish-5-platform/module-page-not-found-error