Post-fix: The test case pushed with the fix had each node
acting as slave to the other two nodes with different set
of filters on server_id's. The slave's gtid_slave_pos is
updated after it processes the events received from master
nodes irrespective of whether the events were filtered
or not. Thus, sync_with_master_gtid.inc could unblock even
on filtered events.
As a result, sync_with_master_gtid.inc would fail to block
until the desired changes have been replicated.  Fixed by
simplifying the topology.
Also, modified CHANGE MASTER commands to ignore based
on gtid_domain_id instead of server_id.