+con #15157 Changed ClusterSharding.start to return the shardRegion
ActorRef #15209

* Changed ClusterSharding.start to return the ActorRef to the shardRegion (#15157)

* Fixed indentation, and removed unused import

* Test for new API
* removed unused import

- Moved barrier outside of the runon

(cherry picked from commit 619585c50e5801c1b79a39df6df770545cf9fbf4)
Merge pull request #15254 from akka/wip-15157-clustersharding-start-API-backport-patriknw

+con #15157 Changed ClusterSharding.start to return the shardRegion (for validation)