Query classifier ignored implicit commits in cases of write commands. Fixed it.

Added more tests for transaction support. Mostly different cases where some command triggers implicit commit in the middle of transaction.

server/modules/routing/readwritesplit/test/test_implicit_commit6.sql

@@ -0,0 +1,11 @@
+USE test;
+DROP FUNCTION IF EXISTS hello;
+SET autocommit=0;
+BEGIN;
+CREATE FUNCTION hello (s CHAR(20))
+RETURNS CHAR(50) DETERMINISTIC
+RETURN CONCAT('Hello, ',s,'!'); -- implicit COMMIT
+SELECT (@@server_id) INTO @a;
+SELECT @a; --should read from slave
+DROP FUNCTION IF EXISTS hello;
+COMMIT;