WL#7592 step 15.2. GTIDs: Generate Gtid_log_event and Previous_gtids_log_event always. Run suite with GTID_NEXT=ANONYMOUS.

This adds functionality to the mtr test framework scripts that allow
running the replication suite with GTID_NEXT='ANONYMOUS' in all
connections. This is to provide very good coverage for the logic of
anonymous ownership.

Conflicts:
	mysql-test/include/master-slave.inc