Clustering:ShardManager does not return the leader of the Shard in FindPrimary

In ShardManager's FindPrimary, it attemps to return a shard replica , which may or may not be the leader of the shard.

The logic to return it from the local exists, but to find the actual leader of the shard is missing.

For a 3 node cluster, this might not be introducing a significant dent in the performance, as each node has atleast one replica of each shard.

But when we move to more fine-grained sharding, the number of hops will be 1 more.