agg_out.js concurrency workload always fails to shard the output collection

The concurrency workload jstests/concurrency/fsm_workloads/agg_out.js runs aggregates with $out and will rarely attempt to shard the output collection with the key: _id: 'hashed', expecting all subsequent aggregates to fail.

The workload's first state inserts to the output collection and sharding a populated collection requires an existing index matching the proposed key, but the test does not create a hashed index on _id in the output collection, so every attempt to shard the output collection fails with InvalidOptions, which isn't caught because the test does not assert the shardCollection command succeeds.