Problem:
========
When the mysql.gtid_slave_pos table uses the InnoDB engine, and
mysqld starts, it reads the table and begins a transaction. After
reading the value, it should end the transaction and release all
associated locks. The bug reported in DBAAS-7828 shows that when
autocommit is off, the locks are not released, resulting in
indefinite hangs on future attempts to change gtid_slave_pos. In
particular, the transaction was not properly finalized because
thd->server_status was not updated to reflect the end of the
transaction.

Solution:
========
This patch updates the code to properly commit the transaction after
reading gtid_slave_pos during mysqld start-up.

Reviewed By:
============
Andrei Elkin <andrei.elkin@mariadb.com>