This fixes#899. In that issue, the primary is cluster-allow-replica-migration no
and its replica is cluster-allow-replica-migration yes.
And during the slot migration:
1. Primary calling blockClientForReplicaAck, waiting its replica.
2. Its replica reconfiguring itself as a replica of other shards due to
replica migration and disconnect from the old primary.
3. The old primary never got the chance to receive the ack, so it got a
timeout and got a NOREPLICAS error.
In this case, the replicas might automatically migrate to another primary,
resulting in the client being unblocked with the NOREPLICAS error. In this
case, since the configuration will eventually propagate itself, we can safely
ignore this error on the source node.
Signed-off-by: Binbin <binloveplay1314@qq.com>