informant: display I/O stats (#11523)

* informant: collect I/O stats for state_db

* informat: debug i/o log

* informat: remove unused cache hit ratio

* Cargo.lock: cargo update -p librocksdb-sys

* [deps]: upgrade kvdb-rocksdb to 0.6

* Update ethcore/types/src/client_types.rs

Co-Authored-By: David <dvdplm@gmail.com>

Co-authored-by: David <dvdplm@gmail.com>

parity/informant.rs

@@ -257,6 +257,14 @@ impl<T: InformantData> Informant<T> {
 			(diffed, full_report)
 		};
 
+		debug!(
+			target: "io_stats", 
+			"{} reads, {} writes, {} transactions",
+			client_report.io_stats.reads,
+			client_report.io_stats.writes,
+			client_report.io_stats.transactions,
+		);
+
 		let Report {
 			importing,
 			chain_info,