MetricsHistoryHandler: don't query .system collection

The MetricsHistoryHandler queries the .system collection on startup with a match-all-docs query just to see that it exists. I think we should do this without actually issuing a query, like use ClusterState. Ideally SolrClient.getCollections(regexp) would exist but alas. In CloudSolrClient, it'd work via cluster state. No query needed!

It's death by a thousand cuts in our Solr tests. In tests, I wish Solr features like this were opt-in.