FR: Allow to start old-style replication even if mysql.rpl_slave_state is unavailable

Currently if the server is started without InnoDB (while mysql.rpl_slave_state is already created as InnoDB table), it's impossible to run replication even without GTID. On start the slave produces

Last_SQL_Error: Unable to load replication GTID slave state from mysql.rpl_slave_state: Unknown storage engine 'InnoDB'

It's not such a big deal (hence the 'Trivial' priority), but the error looks weird and is likely to cause complaints, because GTID wasn't enabled, and is not very user-friendly, because the only way to proceed seems to be to restart the server with InnoDB, alter the table to MyISAM, and restart the server again, now without InnoDB, which altogether might be time-consuming, and all that while the user doesn't even use GTID.

I suppose it might be possible just skip using mysql.rpl_slave_state (possibly with a warning) when the slave is configured without MASTER_USE_GTID and the table is not available.