Fix Endpoints and ServiceAccounts handling in federation controller

When I was working on OSSM-1962, I noticed that federation controller incorrectly handles Endpoint and ServiceAccount object, so that ServiceAccounts might be empty and Endpoints might not be found.

For QE:
I think that it won't need any additional tests, because this bug depends on order of IPs and ports returned by Kubernetes API and since users have no control over internal data order, it cannot be reproduced deterministically. Our integration and automated tests are sufficient.