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_commit1.sql

@@ -0,0 +1,8 @@
+DROP DATABASE If EXISTS FOO;
+SET autocommit=0;
+BEGIN;
+CREATE DATABASE FOO; -- implicit commit
+SELECT (@@server_id) INTO @a;
+SELECT @a; --should read from slave
+DROP DATABASE If EXISTS FOO;
+COMMIT;