Disabling a user as an administrator removes management console access but
does not remove permissions on exchanges.  If the gues user is not an admin
user we remove their permissions.

THIS DOES NOT WORK DUE TO THE INABILITY TO HANDLE THIS IN THE PROVIDER!!!

It's here to note that this is something we need to handle.  Possibly we
should even have the interface allow the ability to change the gust users's
permissions.
Add ability to define a rabbitmq_admin_user who will perform exchange
manipulation on behalf of puppet.
Fail if we lack a user for the rabbit_exchange provider to use.