PR value set in bucket type ignored when reading data.

We set PR to 4 but unfortunately it is ignored by get_fsm.
https://github.com/basho/riak_kv/blob/develop-3.0/src/riak_kv_get_fsm.erl#L313

It caused data loss, because we got data from non primary vnodes what leads us to not found, we created a new object and overwrite it.