#802: DB2 did not drop triggers on clean

Trivial implementation.
In a former project, I worked around the problems with ADMIN_DROP_SCHEMA by explicilty using not ERRORTABLE as target but a temporary table with a generated name. This should work well with flyway, when the name generation is good enough (fw_<schema> should be sufficient, since no two instances of flyway can operate on the same schema at the same time anyway). To be on the safe side, with could check for the existance of the table beforehand and drop it.

I think I will give it a try and create another pull request, if everything works as intended.

For now, a custom version using my pull request at least solves my specific problems (i.e. migrate-clean-migrate works again).