erp5: fix frontend slave request
- overwrite slapos.cookbook:request.serialised with slapos.cookbook:request
The reason of this change is due to a problem occurred while asking erp5 to request a frontend slave itself. If the request is serialized, the xml parameters for frontend slave request are passed as json: "_" : {...} It seems that the parameters are expected to be passed one by one, so with the serialized request they are wrong parsed and the instance fails. Overwriting the request, the parameters are passed one by one to the frontend slave and it is correctly installed.
/cc @rafael