Also send Refresh and Flush actions to relocation targets

Currently we send relocation & flush actions based on all assigned ShardRoutings. During the final stage of relocation, we may miss to refresh/flush a shard if the coordinating node has not yet processed the cluster state update indicating that a relocation is completed *and* the relocation target node has already processed it (i.e., started the shard and has accepted new indexing requests).

we have this logic also in IndexShardRoutingTable (and when we build the RoutingNodes), maybe we can add a method to shardRouting to create the respective relocating initializing shard so we centralize it?