Statement timeout + replica imbalance fix (#122)

* Statement timeout

* send error message too

* Correct error messages

* Fix replica inbalance

* disable stmt timeout by default

* Redundant mark_bad

* revert healthcheck delay

* tests

* set it to 0

* reload config again

src/errors.rs

@@ -11,4 +11,5 @@ pub enum Error {
     AllServersDown,
     ClientError,
     TlsError,
+    StatementTimeout,
 }