Replicated log: Generate unique opid after process restart

[deepthidevaki]

Now if rep_vnode restarts, opid is restarted from 1 which assigns duplicate opid to new updates which makes these updates invisible.

[cmeiklejohn]

Long live, basho/riak_kv#679.

[russelldb]

Well no, this more the case of we persist the vnode_id and create a new one in riak in the vnode, isn't it? More fundamental the 679. You require disk corruption of riak_kv 679

[bieniusa]

At master, we are not replicating the log (for the moment being).