Fix the createOrUpdate function

As said in #704, this function doens't work and I even think it never has worked... (or for a short time)
This function is accessed by the ContactsManager in core. 

cc @DeepDiver1975 


The `getAddressbook` function returns `OCA\Contacts\Addressbook` (https://github.com/owncloud/contacts/blob/fix_704/lib/addressbook.php#L167) The getChild function returns a `OCA\Chat\Contact` object.