Add shard shutdown functionality to odl-mdsal-lowlevel-control model

There are testing scenarios, where we want to simulate shard failure on some node in cluster. There is already remove-shard-replica rpc, however it's not really suitable for all cases. remove-shard-replica not only shuts shard down on specified node but also changes raft configuration on other nodes.

Implement rpc that just shuts down shard on specified node.