this is an idea shalin proposed as part of the testing for
I created a TrackingShardHandlerFactory which can record shard requests sent from any node. There are a few helper methods to get requests by shard and by purpose.
I will likely move the TrackingShardHandlerFactory into its own issue because it is helpful for other distributed tests as well. I also need to decouple it from the MiniSolrCloudCluster abstraction.