- when mtr.pl is run with the --mysqld=--log-bin option all tests
   will run with binlog enabled. This causes the mysqld(s) to print
   incident events to the binlog when they loose connection to cluster.
   They will also print a warning to the log files which is detected by
   mtr.pl and causes the test to be reported as failed.
 - fix by adding suppressions for this expected error message to
   the affected tests
 - improve comments of ndb_disconnect.test and remove unnecessary
   drop table if exists