Update Shoot/ProductInventory to go against the new keycloak backend

use the new backend from https://github.com/corinnekrych/aerogear-backend-cookbook/pull/1
in README instruction
https://github.com/aerogear/aerogear-ios-cookbook/tree/swift/Shoot
we refer YYY to client_id
and XXX to client_secret
Could we keep the fbYYY to follow instruction