enclose asserts in a try/finally to make sure that even after an error,

the bt will be uninstalled. This makes sure that test_type_provider_2 is
not contaminated after a failure of test_type_provider


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@39497 20353a03-c40f-0410-a6d1-a30d3c3de9de