test: Cleaner way of intercepting failures in MachineCase
test: Cleaner way of intercepting failures in MachineCase

We want to intercept failures in MachineCase so we can download
the journal and core dumps. Do this in a simpler cleaner way.

This also lets us do this using standard functionality and catch
the resulting errors with the retry logic.

Reviewed-by: Dominik Perpeet <f7830b2723a5db4fc185058b06cfab4b89a38da9@redhat.com>

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