Fix sync committee penalty tests on #2453

[hwwhww]

This PR is based on #2453

1. cherry-pick Align Sync Committee Tests to Specs #2461 changes (Thanks to @potuz)
2. [Refactoring] Move some helper functions from test_process_sync_committee.py to eth2spec/test/helpers/sync_committee.py
3. Fix the tests by including the sync committee rewards and penalties.
   • We have some assertions that check if the result balance is expected. Now Modify sync committee logic and parameters to reduce variance #2453 introduces new per-block rewards/penalties so we have to compute them.