Dont cache prepared statement with errors (#647)

* Fix prepared statement not found when prepared stmt has error

* cleanup debug

* remove more debug msgs

* sure debugged this..

* version bump

* add rust tests

src/errors.rs

@@ -29,6 +29,7 @@ pub enum Error {
     QueryRouterParserError(String),
     QueryRouterError(String),
     InvalidShardId(usize),
+    PreparedStatementError,
 }
 
 #[derive(Clone, PartialEq, Debug)]