The only purpose of BaseServiceHandler is to handler broken/timeout/... events, and this behaviour is required during verification stage to raise VerificationFailure exception when a storage node required is lost. This was found by failing unit tests.

git-svn-id: https://svn.erp5.org/repos/neo/trunk@1419 71dcc9de-d417-0410-9af5-da40c76e7ee4