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>

ethcore/verification/src/queue/mod.rs

@@ -234,7 +234,7 @@ impl<K: Kind, C> VerificationQueue<K, C> {
 		let number_of_threads = if scale_verifiers {
 			max_verifiers
 		} else {
-			cmp::min(default_amount, max_verifiers)
+			default_amount
 		};
 
 		let state = Arc::new((Mutex::new(State::Work(default_amount)), Condvar::new()));