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).

same as the previous comment to centralize the creation of initializing relocating shard