This worklog aims at adding a new sql function WAIT_FOR_EXECUTED_GTID_SET which 
make the current syncing option for the slave with master independent of the 
slave threads. 

The use of the new function will be :

WAIT_FOR_EXECUTED_GTID_SET(GTID_SET [, TIMEOUT])

Wait until all the transactions whose global transaction identifiers are being 
specified, are contained in gtid_set.

ie. After this function returns with success, it must hold that 
    GTID_SUBSET(GTID_SET, @@global.gtid_executed) returns true.