Fix creating orders for other users using the pizza API

Ghost User
2017-11-22T20:41:57+01:00

#### Previous behaviour
Steps to reproduce:

1. Be an admin and have an active pizza event + products.
2. Create a new order for a user that is not you using the API.
3. The order is created for you.

#### New behaviour
Steps to validate that it works:

1. Be an admin and have an active pizza event + products.
2. Create a new order for a user that is not you using the API.
3. The order is created for the specified user.