test: improve the failure test case
test: improve the failure test case

We wait for the `perform` call to actually fail the first time, before
shutting down and retrying.

This test currently blocks forever because a failure processing the
journal kills the thread which checks for shutdown requests.

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@citrix.com>

jonludlam/shared-block-ring,djs55/shared-block-ring,simonjbeaumont/shared-block-ring