The current FailureHandler mechanism was fairly opaque with regard to the
failure reason due to using CHECK(0). Scudo is a bit different from the other
Sanitizers as it prefers to avoid spurious processing in its failure path. So
we just dieWithMessage using a somewhat explicit string.
Adapted the tests for the new strings.
While this takes care of the OnBadRequest & OnOOM failures, the next step
is probably to migrate the other Scudo failures in the same failes (header
corruption, invalid state and so on).