Problem & Analysis:
===================
When relay log info repository is configured to be persisted in a
table, it is updated when transaction commits or explicit flush is called,
like on relay log rotate. If a transaction that uses non-transactional
engine is split across multiple relay logs, on relay log flush
it will be partially committed. If GTID_MODE=ON and when partial transaction
in first relay log is committed, it uses the current GTID value and sets
GTID value to UNDEFINED GROUP. Hence it causes 'ER_GTID_NEXT_TYPE_UNDEFINED_GROUP'
error when it is trying to commit the rest of the transaction.
It also causes many other problems if the repository is updated in between
the transaction and it should be avoided.

Fix: relay log info repository should be updated on relay log
rotate. But when the transaction is split across two relay logs,
update the repository will cause unexpected results and should
be postponed till the 'commit' of the transaction is executed.

Introduced a flag that set to 'true' when this type of 'forced flush'(at the
time of rotate relay log) is postponed due to transaction split
across the relay logs. And the flag will be checked in flush_info function
to see if there is a flush that got postponed earlier. If so, it will
force the flush now irrespective of sync_relay_log_info value.