PersistFinalizationCertificate should increase to proper round

[samliok]

I believe we have a bug in this scenario

1. All nodes start at round i.
2. A couple consecutive empty rounds occur, say i + 5
3. Some node n may still be at round i or a round less than i+5, in the case they were lagging or dropped emptyVote messages.
4. All nodes receive a finalization for round i+6.
5. The lagging node n will see that the finalization for round i+6 is the next sequence to commit. It will commit that fCert and increment the round by 1.

In this case, the lagging node should increment the round to i+6 rather than i+1. This will cause it to be out of sync when receiving proposals, votes, etc... for the subsequent rounds.

[yacovm]

The lagging node n will see that the finalization for round i+6 is the next sequence to commit. It will commit that fCert and increment the round by 1.

It shouldn't increment the round. We only increase the round because of an fCert once we also index a block to the storage.
So if the lagging node sees that round i+6 is the next sequence to commit, it must have committed all blocks prior.