Bug#46527 COMMIT AND CHAIN RELEASE does not make sense
Bug#53343 completion_type=1, COMMIT/ROLLBACK AND CHAIN don't 
          preserve the isolation level
Bug#53346 completion_type has strange effect in a stored 
          procedure/prepared statement

Added test cases to verify the expected behaviour of :
 SET SESSION TRANSACTION ISOLATION LEVEL, 
 SET TRANSACTION ISOLATION LEVEL,
 @@completion_type,
 COMMIT AND CHAIN,
 ROLLBACK AND CHAIN
 ..and some combinations of the above