Fixes #6367 - let superusr client_auth? BZ1112664

fixes the ability to register using subscription-manger using the
consumerId flag with the admin user by:

1. giving users that have the superadmin role the ability to act as a
consumer, so that admins can register using subscription-manager with
the consumerid flag.
example: register subscription-manager register
--consumerid 51a5c720-dfd4-45ae-9664-712828ead937 --force

2. calling authorize prior to the consumer_show action
Why make this superadmin specific? Anybody should be able to register a consumer specifying the consumer ID given the proper permissions should they not?