Investigate reward calculation in Shelley genesis

[Lucsanszky]

A user reported a recent change in behaviour for reward calculation in Shelley genesis for cardano-ledger-shelley ==1.17.0.0. Investigate what caused the change, create a reproducer test and create a fix (if needed).

[kderme]

A reproducer I currently have is a ci failure of test rewards simple here.
The test uses this genesis file
It initially registers all pool reward account and pool leaders.
It wait a few epochs
And counts the rewards