Change type of replicaID and Epoch

[yifan-gu]

For replicaID, we can keep it uint8 now, because we will change it to UUID ultimately.
But I am wondering if we wanna change Epoch from uint32 to uint64... Raft seems to choose uint64 for Term.

[hongchaodeng]

Term (Raft) is different from Epoch (Epaxos).
I think either one is good enough.