Validator clients should be able to GET / DELETE itself
Normal and Validator clients should be able to update themselves

 - Admin clients can update themselves and anyone else
 - Validator clients can downgrade to normal client, but not upgrade to
   admin client
 - Normal clients cannot upgrade to admin or validator client
 - Validator and normal clients can update themselves
 - Validator and Normal clients cannot update anyone else
 - A user with the same name as a client cannot update that client
Merge branch 'hh/CHEF-3697/admin_and_validation_clients'