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 


Since the method returns a Card object (https://github.com/owncloud/contacts/blob/fix_704/lib/carddav/addressbook.php#L210) it wouldn't be so bad to have it named $vcard